He doesn't say which platform the devs were on, he just says to leave both those behind because they're both the same type of CPU. Like if I made a tweet talking about how partisan the Democrats were acting then said "it's time to leave behind the two party system" and you went A-HA, he has a problem with how Republicans are currently behaving, too!
Either way, the PR around Series X has been that the games will be cross-gen, that being cross-gen won't hold them back. The PR for PS5 has been about believing in generations and not being interested in making games work for PS4. It's beyond clear why people are assuming this is more about one platform than the other.
The tweet specifically mentions both Xbox and PS4. Both of them. Each one of the two systems. Equally.
The 'PR for PS5', exactly. They're will be cross-gen games on the PS4/PS5. The same issues will apply for those.