My pet theory is that this was said specifically to destabilize the US. As others have said, this is not new. China has been saying this for a long time. But 100% the GOP is going to call Biden weak for not shutting Xi down and instead saying the US supports a "One China Policy " without any critical thought as to what the dynamics are.
This is to fire up the right wing base.
It's not about how people vote. It's about getting people to vote. Emotionally charged people are more likely to vote/volunteer/donate etc.
I'm talking out of my ass by the way, I have nothing to prove any of this.