That’s a fair point. Although I’d point out that the Ghiscari are also Valyrian in heritage, and have been so for several thousand years.
*cough* Oh yes, quite.
The gods of Ghis were dead, and so too its people; these Astapori were mongrels, Ser Jorah said. Even the Ghiscari tongue was largely forgotten; the slave cities spoke the High Valyrian of their conquerors, or what they had made of it.
A “mongrel” culture, whose dialect is referred to in an incredibly unflattering way… they are not remotely Valyrian the way Dany is Valyrian, she does not see them that way and they only see her as a Westerosi.
(“Mongrel” is used to refer to the Ghiscari 5 times in ADWD. They are othered and animalized by the characters and the narrative, and it is certainly deliberate.)
Sure, they call themselves something else. But we’re also told that “the colossal pyramids and temples and homes were given over to dragonflame. The fields were sewn with salt, lime, and skulls. Many of the Ghiscari were slain, and still others were enslaved and died laboring for their conquerors.” And then the Valyrians settled their lands and occupied them for five thousand years.
And then 300-400 years ago, they made up a new culture and claimed to be the same as that old culture. Does that make them the old culture?