This is actually a very good piece of information in favor of Jung being an INTP. However, there's a few contingencies that could point the other way:
1. We don't actually know if Carl Jung knew his own type (and he founded the theory so you would think he should, but it's not a fact).
2. He may have been playing a game with us. Just because someone says one thing doesn't mean that they aren't really thinking something else.
3. Maybe under his own set of definitions in his context he really did fit the category of an INTP, but perhaps the system he was using was incomplete and lacked proper classifications.
4. He has not only claimed to be an INTP, but he's also claimed to be an ISTP, as you can see in the
Jung identified himself as both INTP and ISTP link.
Ultimately, you can choose to see Jung from what you perceive to be a factual standpoint as an INTP, but it doesn't change the reality of what type he really was, except in your own ideology.