Proof? The news I recently saw, if you're referring to that, actually said they'd offer a higher-bitrate 1080p option for YouTube Premium, not that they'd lock the (then) current bitrate behind YouTube Premium and downgrade everyone else.
Edit: I did some searching. In addition to that, the only relevant news I could find were about Google testing locking the 4K (2160p) resolution behind the Premium doors, which they ceased doing.