“His” as the default gender pronoun is a semi-old-fashioned but very widespread convention.

His at the time meant the same thing as singular they does now.

I think in case of most games, maybe 90% of the already audience (if not more), was male.

It must have been easier to write then his/her game all the time - and also more pleasant to read.

I think it makes/made perfect sense.

It was almost thirty years ago.