Assuming my description of the event is correct (i.e., fair die, fair rolls, accurate memory, etc.)

[looks up how reliable human memory is, how it changes at every recall, how overconfident we tend to be about it]

[looks up a couple of conjuring sites]

Thirty years ago...

Hmm...

I had 26 armies and was attacking the last army of the last territory of one of my opponents... My opponent told me that he usually let me win, but not this time. He'd never said anything similar before.

Hmm...

That experience led me to conclude that reality is far weirder than I had imagined.

I think there might be non-supernatural explanations with a greater than 1 in 100 billion chance. If it's even 1 in a million, you'll expect to see at least one in 30 years.