It's hard to find videos of him just... talking. All this hands-on experimental stuff seems very Sensor to me. Doing science doesn't mean he is Intuitive.
So there's this video, where his energy is of a different type than ISTJ I would say, but that's only for like 40 seconds:
https://www.youtube.com/watch?v=UlAAhRlqlV0
In this video he's using a lot of Te, so I could see why you might say INTJ:
https://www.youtube.com/watch?v=FiqLBXU2f6E
I only skimmed through the above video though, so all I saw was Te, I didn't get a strong read for either Ni or Si (though he still seems introverted)
[I'll add more later]
edit:
Alright, so this is the final video that I will look at:
https://www.youtube.com/watch?v=EZrxfTUPxCE
You see in this video, again he starts with Si. He recounts his day, he compares his weight from his weight a few days prior. Then, as he exposes the chainmail he makes a comment about returning to Earth, and here you'll see he starts using a more Te heavy process, that is, his speech becomes more centred around processes. Following that, he again makes a mention about returning to earth, and you'll see that here his Fi kicks in. As he loosens up, he becomes more happy, and you'll notice he is still saying things that relate to Si and Te, however with a clear increase in emotionality.
The video seems to end abruptly, lacking use of the inferior function to clear it up. This video is from 2013; by his recent videos, he is using Ne much more fluently.
So, I will keep my typing as ISTJ for him.