I consider the lockdown/last post a bit of a "went over the threshhold, enough of this", though a bit undiplomaticly shortcut in the wording.
And - to my knowledge (which is of course only "passive reading of books"), the aging Tesla was very short on money and success - and secured further funding by even more (ridiculous) claims, that he did not fulfil, nor was (technically/physically) able to fulfil, ever. This certainly qualifies him as charlatan, IMHO. You could also say he duped investors, commited fraud etc pp.
This is very much the reason why I believe Simon was rightfully naming him a charlatan.
However there are some inventions of him, that clearly showed his great talent at younger age.
Some say he suffered from mental problems, I could believe that.