Okay so, a primer:
“high elf” as a race are the descendants of the Highborne that traveled to the EK. Currently, Blood Elves, Void Elves and High Elves as political groups all fall under the “high elf” race. Some of them are infused with fel, light or void, but genetically they are still the same race.
High Elf, on the other hand, as a political entity, was the whole of the race, but they have splintered since the 3rd War with the majority renaming themselves Blood Elves and joining the Horde eventually, and later a group of them became Void Elves and joined the Alliance.
Of the remaining minority after the Blood Elves came to be, most of those High Elves remained on human cities due to their once affiliation with the alliance during the 2nd War, particularly the case with Dalaran and its high elven population; others in isolated lodges across the EK, in good terms with the alliance as well. Others such Alleria and her Farstriders were stranded on Outland. And of course some neutral High Elves here and there.
With Dalaran becoming neutral during WotLK, it’s population became more polarized. With the city itself becoming neutral, a group of High Elves lead by Vereesa became militant in support to the alliance, and were against blood elven and Horde inclusion in Dalaran,
Ultimately, Alleria returned during Legion, and joined the recently created Void Elves as one of their own, and leader.
So are Void Elves High Elves? Depends if you are looking at elves as a biological group, a species, or an ideological or political party. Biologically they are all the same, or as distinct from each other that if you consider one not a “high elf” might as well do the same with the others.
Politically speaking, High Elf currently makes reference to elves that didn’t follow Kael’thas after the 3rd War and didn’t rename themselves Blood Elves, and can either be Alliance, Neutral or in some specific case even aligned with the Horde.
Now, the fact that Void Elves are made of once ideologically Blood Elves, lead by a High Elf, joined by both Blood and High Elven students, makes the whole thing even more complicated. Currently Void Elves are still that initial group of Blood Elves that started delving into the Void, lead by Alleria. But by Midnight I’m confident we will get a bit more expansion on them and see how they have been recruiting new members.