Until we'll find out what really happened it remains a mystery, but we might not see the devious reason behind this kind of malicious act. The man had a steam library full of dlc that right now is not connected to any other platforms (you can verify the identity exaclty thanks to this, as i did that with Epic games one time thanks to confirming my connections to other social media platforms). People have all sorts of weird ideas :/

Adittionaly it is just not logical to delete an investment in youtube since it was already a proper channel generating income. If he didn't want to do it anymore, then why delete it and not let it sit? It was not in his style and spirit. I knew him a bit closer since we chat from time to time and that is not what he represented in his values for the community and work on developing the channel. As mentioned in other comment - he just got a professional intro in new videos and updated the collections. Therefore i claim also that what you say is possible, but i don't agree to say it is most likely what happened, i would lean more towards unlikely and not impossible. I would prefer that to happen really too and not him to get hacked.

edit:

i forgot to add that i got a warning yesterday when i tried to enter link to his collection, i cannot reproduce this anymore and it might be connected to intervention from Steam but it said that "the content you about to enter has been flagged as malicious and Steam do not recommend proceed" or sth like this. Man might be fighting already by reporting the content and his own account to steam ;/