I think it is MORE likely that a retinue manages his Twitter account. Ms Jay was probably followed by some (now unemployed) denizen on Team Obama as a joke.
FWIW, Trump is following only forty-six accounts.
This makes sense.
Weren’t there reports that millions of obozo followers didn’t exist? Nonetheless, your explanation is plausible though it would be good to ask him about it, and how they manage who he is following, and will he dump her now that he knows. 600,000+ seems quite high. 200 could keep a person really busy.