Yes, he was a beta tester on a game he never posted an article on.
Here is one of the instances where he praised it explicitly: https://archive.today/NeJis#selection-387.664-391.0
"Anyway, standouts: powerful Twine darling Depression Quest, [...]"
Praising a game one is involved with first out of three out of 50 definitely warrants a quick one-sentence disclosure blurb. Slamming it would too. In any other case that's not just forwarding a plain alphabetical list, it would be at the very least good form to do it.
If a journalist reports on something they have an unexpected relation to they have to disclose that to their readers. Otherwise they aren't doing their job properly (e.g. according to http://www.spj.org/ethicscode.asp, but that much really should be common sense).
It's true that this one in particular isn't his largest undisclosed likely conflict of interest, but outright denying it exists is ridiculous if the evidence to the contrary can be found relatively quickly.