While I can't assess his claim (mostly because there's no evidence provided) I can tell you that I'm extremely skeptical that it's anything more than propaganda. Contrary to what the people in the thread say, we do actually have a pretty decent record of the time, between Japanese, Chinese, and Soviet resources. We have people who attest to his basic biographical details, including his superior Zhou Baodong, as well as Japanese soldiers from the Kwantung Army. Andrei Lankov goes over the evidence in his book From "Stalin to Kim Il Sung: The Formation of North Korea," if you want to read more about it.

I for one am more curious about the claim of Tito being an imposter.