Playing *cough* Devil's advocate, I'd have to say that the researcher didn't offer any proof of Jesus' existance. He or she just relied on the extant, highly debated material that many people refuse to believe proves His existance.
The only way this could mean what you say is if the researcher found something outside the body of work we already have, physical evidence or a new, non-Christian historical reference, etc.
Don't get me wrong, I'm a 'believer', but people could debate the cause of death for fictional characters in the same way, and it wouldn't lend to the idea they really existed.