you mean that dark trolls who look like trolls, look like bwosandi, when he literally look like a troll?
I don't know where the "bwosandi was a dark troll or a sand troll" stuff came up but that would not make any sense in the lore ashow the tribes wre created/evolved a long troll history.
First they said/implied that Bwosandi predate even the zandalari, meaning he was probably part of the first trolls who later would create the zandalari empire which other tribes would evolve from, the dark trolls were not part of then since they themselves have evolved from other troll tribes
sand trolls came from the jungle trolls,
after aquir wars, Dark trolls while already existing in the aquir wars
were stated to be blue, before going purple skined with their underground lifestyle, and taking account they just mention
color changing, and not physicall change, is more likely that, just like sand trolls, dark trolls came from a branch of jungle trolls who dwelve deep in this area
Bwosandi is supposed to be older than that.