[Rygar]

Just for the casual bug report skimmer, here are the relevant quotes I found from your link:

Oct 09 2001
Well I have seen a few mention that this mob , along with others , are hard to catch and finish bc of them being sowed. Heres a trick I have learned , it has worked with anything I have tried it with , when he starts running and you cant keep up for some reason just sit down , he will think you are an easy mark and come back for you . When he is in range stand back up and hit him , continue if needed til your able to keep up . Of course not always an option if you have to becareful with adds .

Oct 10 2001
Oppss , meant in the last stages of battle while he is running away with not much health , if hes sowed its hard to keep up . Thats when sitting down will help , he comes back to you when your sitting wether 1 hp left or more, still will come back.

I've been gathering some evidence on NPC flee mechanics, and since you've posted this I'll share some other links I found as well. I came across a mention of sitting to get a mob to come back and I was skeptical, but now your mention makes me believe it is a thing. However, best I could guess is they would only turn around if the top person on the hate list would sit. I was a tank myself and many times the mob would flee but not whack a caster sitting down. I never knew about this mechanic myself back in the day, I've no clue if it is like this today on live or was patched out and at some point.

3/9/01:

If you are in a dungeon and a MOB gets away DON'T chase it unless its
almost dead and you are sure you can kill it in a couple of hits (rogues
are good for this). MOBs only run a certain distance away and stop, but
they will keep running if you keep chasing them. They will run through the
dungeon bringing a train back down on you. A good trick to use is to sit
down, this will bring the running MOB back to you. Nukers don't be shy
about dropping those runners, better that you over burn on them than to let
them bring a train back on you.

I also bolded the portion about them running only a certain distance (my best guess is somewhere between 200 - 300 units), as I was looking into that too. Found more support for it:
9/7/99:

A few days ago I was in CB and seen some one using a bow and arrow hitting a
guy and it died standing there it didnt even move. Is this a big or are the
orcs just dumb? thanks

Note that some rightfully claimed this mob could have been snared or rooted, but others chimed in about them only fleeing a certain distance and stopping.

I have noticed in the swamp when playing my Troll, when a Froglok gets down
and health and runs, sometimes it doesn't run far enough away to be out of
bow range. (They run away and sit to gain a bit of health before attacking
again) I have killed quite a few with a bow that way, because they don't
start coming back towards you until they get a certain percentage of HP
back. If you keep hitting them with arrows, they will stay put. Not really
sure if this is a bug, but if I see my enemy sitting there I really hope
Verant doesn't expect me to sit down and wait for it to come back and get a
few cheapshots in!

Araknus
Troll Warrior lvl 10, Innorruk

Note that poster is a Troll warrior so snare is not in play, and mentions the faster state of HP regen. Another poster backs him up on it not being a root/snare thing:

I have also noted this behavior with gnolls when I am the only one around so
root/snare is not an issue. The original poster is correct....some creatures
will run away and stop in bow range trying to heal but can get struck with
arrows or spells. The place I have noted this is in BlackBurrow at the first
bridge when you go downstairs.

Not sure again if this is in play on live today or patched out at some point lost in history, but there are mentions of it being around in 1999 and 2001. Just was hoping to get more posts mentioning this.

I know this is not in play on P99 as I have seen Jaeil the Wretched get aggroed in a raid and sent into flee mode in the Hole, and he ran up to the pit drop off area, which is a huge distance. To be clear, if someone on his hate list was following him the whole way this would be possible, but no one was. I believe the mobs were just coded to only flee up to a certain distance away from nearest PC on hate list.

But back to the original subject of sitting to bring a fleeing mob back, I am indeed thinking this was a thing, but would be nice to find more than 2 posts on it (and not sure if staff would view it as exploit potential on unsnareable / unrootable mobs).