Lots of people knew about this statement. Serebii has known for months. The reason it was never really brought up here, on the main site, anywhere, is exactly because it essentially boils down to "unnamed, unidentified source mentioned this highly "controversial" spoiler on the internet with no real proof", and it would just create a bunch of arguments over its validity.
But yeah, it's been out there for a while, it's not some obscure knowledge shared by only one or two people. It's just the kind of thing people have individually decided is better to keep quiet about until we know more.