So I did that Riekling quest, , and I had the option to get a Riekling as pet. I let one follow me around the mead hall for a bit but he wasn't worth the hassle so I dismiss him.

But now almost in every battle I went in there's a pack of friendly Rieklings appears out of nowhere helping me, and when battle's finished they just stood there, still have the option to have one Riekling to follow me. And later the pack appears again, fought for me and stood still when I'm done fighting.

It's nice to see reinforcements, but many times my stealth attempt was messed up as the Riekling pack just appear from nowhere and march straight into the enemies. I tried killing all of them, but they just appear again later.

Is this a bug? How do I get them off my back!?

not a bug, its just what happens if you help them

and how does that mess up your stealth play?
unless you have a super low sneak skill, you should remain mostly hidden even if rieklings appear and start fighting bandits youre sneaking up on or around

and they shouldnt appear much
i get them about once every 10 fights or so, and only on solsthiem
not really anything to hate on in my opinion

I usually like to sneak up on bandits to take their clothes and weapons and poison them or cast frenzy. These Rieklings just appear out of nowhere and charge the bandits the moment they're suspicious I'm around. Sometimes the rieklings themselves were hit by Frenzy and after standing still for a couple second they start to attack me.

I would probably try killing all of them in the mead hall and see how things go, because they get really annoying!

One of my characters, Braggen also has the over enthusiastic pests, he has not resorted to trying to kill them off yet, but they are making themselves unpopular. One character (Rork) could do with the extra help, one (Aussie) will take the Nord's side but Braggen would just rather do his own fighting with no hairless ewoks cluttering up the place, they should go stay in their mead hall and get the message they are not wanted.

I killed them all... How dare they take over Thirsk where my Nerevarine character was leading at one point!