It means that it was a true statement, but that reading the statement still tickles the "irony" feeling in your brain.

I think part of the reason that this is so is that some people sympathize with this mathematician's motives. An analogy:

"He donated $1,000 to charity, instead of donating his entire discretionary income."

"How utterly selfish of him."

It's true that it's selfish, but it's a lot less selfish than what most people do, so it feels ironic and sarcastic that we are calling him selfish.