That's not an ad-hominem because he wasn't using it to support another point. He has every right to avoid being around negativeness. If you think that this attitude isn't doing him any good, that's also YOUR opinion and he has every right to disagree without being accused of a non-existent logical fallacy.
That's just a gratuitous ad-hominem.
If you are terrified by the thought of putting your work out there for others to judge, I suggest that you work on that problem.