In World of Warcraft:Legion, we run into vrykul, tauren, and other races that are related to other known races. However we run into different 'tribes' of a race of large bulky humanoids that have tusks (Similar to the troll berserkers) Is it ever revealed whether they are a type of troll, or are they a completely new species?
Nothing official has been revealed about the Drogbar race origins yet. That's kind of unusual, given that there was even an explanation for the Broken Isle's variant on Tauren (yes, moose-antlers have an explanation). So there are plenty of guesses being bandied about.
The more common theory is that the Drogbar are a remnant of a troll clan labeled dark trolls, which are a lore remnant of an underground race that could fit. I don't personally give this much credit, because we've yet to meet a troll clan that consisted entirely of bulky berserker type trolls, and we've yet to see a "small" Drogbar, or anything else that resembles an actual typical troll. Trolls also tend to be fairly clever even among more savage tribes, which is something not seen from the Drogbar. Possibly the final nail in the coffin of this idea, dark trolls are revealed in Chronicle, Vol. 1 to be a more peaceful and harmonious variety of troll that existed in prehistory, and upon moving near the Well of Eternity and soaking up it's energies, slowly became the first night elves. If dark trolls or their descendants did still exist, they would have more in common with elvenkind, not with the brutish drogbar.
The closest fit that I've been able to come up with would be troggs, which are also bestial subterranean creatures, with roughly the same brutish appearance. They also happen to be devolved earth elementals which would explain some of the Drogbar powers quite nicely, and the name even lightly fits in a corrupted language sort of way. The only problem is troggs are far far stupider, and much weaker looking. My counter-thought is that proximity to Neltharion - a giant source of Earth magic, before he got nasty - may have pushed them back in the other direction, giving them just enough wit to assemble a basic society and packing their form with muscle. This is, unfortunately, still a guess, and it's also a guess that could be stretched and applied to just about any race that happened to wander in.
There are some other theories linking them to goblins, but given we've already seen muscled-up goblins (the drudges they sometimes call hobgoblins) I doubt that's in the cards either.