Have you read the article or the report it is based on? I think he makes his point quite clear.

Did you know? Reading the article explains the headline, I recommend doing so… well, to be honest, I recommend reading the report the article is based on.

He says “Indie golden age” since the number of games with 1000 reviews or more made a big jump from 337 in 2022. This is also an increase percentage-wise despite the huge increase in games overall:
This is all games, the article focuses on the indie portion (as decided by the writer, not steam tag) later on.