Or is a conjunction. Black or white, sink or swim.
I disagree with the ruling so I throw in. You win by default Wizards is wrong.
While Thought Prison is kind of an unusual card, that part of it follows a pretty standard template, which is why it's still the same in Oracle text as it is on the original printed card. It has you choose a card and tell you clearly that it's having you choose a card. The part with the conjunction says nothing about you making a choice, because it's templated to trigger on either
condition. If they only wanted it to work on one or the other, they'd template it very differently, instructing you to make your choice at the time you imprinted the card.
Of course, the people at WotC setting up wordings for how cards will function within the rules don't always make things intuitive, and perhaps this is an example of that.