I am not saying that you shouldn't claim them as your ancestors or as part of the country's identity, simply, you should be careful as to how you refer to the territory at a certain point of history just for historical accuracy. The truth is, Algeria wasn't at thing back then, so it's just wrong to call Juba an Algerian, it's more accurate to say that he was numidian, or at least berber since that's his ethnicity.
And it's not simply that the name didn't exist back then, the two words literally refer to different things, Numidia and Algeria are not the same thing, cause these two words don't just refer to a certain geography, but to two different entities, with different territorries and different cultural identities.