> Is it because, as the leader of a language, he shouldn't be making "attacks" against other languages?
Actually, yes. Not only from the angle of common decency or adhering to a code of conduct, but as a matter of professionalism and setting the example for followers.
> as far as V being a fraud...
That is a provably false claim from competitors, who should not be engaging in such activity.
Paying supporters[1][2][3] (ylluminate, gompertz, etc...) of the V language have even gone on record at HN, to clearly state such competitor or evangelist claims are false, and that they are happy with the language.
Not only can such competitor generated claims be seen as false, through direct V supporter refutation, but by the visible progress of the project as a whole. Over the years, the V language repo continually amasses thousands of stars and hundreds of contributors, that can be plainly seen on GitHub. It is a significantly large and successful project. To pretend or argue otherwise, is very disingenuous. People are there, because they like using Vlang[4].
[1] https://news.ycombinator.com/item?id=31801287
[2] https://news.ycombinator.com/item?id=31801262