The fact that he’s hesitant to sign a message to prove he solved puzzle #125 and #130 clearly suggests he’s not being truthful. Plus, if you look at the mini-puzzle he started, it seems suspicious. The user "sneeky777," who solved the mini-puzzle, appears to be Retired Coder himself using a secondary ID. The ID "sneeky777" registered on the same day, October 14th, when Retired Coder posted the mini-puzzle.
https://bitcointalk.org/index.php?topic=5513047.msg64634120#msg64634120He was truthful at least regarding #120. IDK about whether he solved his own mini puzzle, but that challenge was really easy to solve, if I knew what he really meant by it I would have solved it a few hours before the other user, since it was basically something like 20 lines of Python code. I was already checking millions of Bitcoin Cash balances by the time it got solved, instead of simply comparing some public key.
But for 125 and 130 it would cost hundreds of thousands of $ to even pay for the electricity required to solve, no matter how well the program or algorithm is optimized. So he likely has access to a grid, or the keys were known and this is all a big joke on all of us.