

If you use a VPN, you’re always connecting to the same IP
No, you’re not. A VPN provider can have hundreds of thousands of IP:s.
which is unusual
OK, but not unheard of. And even a dynamic IP might remain the same for months, if not years, depending on the operator.
would tend to indicate VPN usage
No, it wouldn’t.
You keep telling yourself that.
Sure, there are some specialized anonymity-focused VPN providers that only have a few IP addresses in order to have as many users behind each IP as possible, but that’s definitely not “most public ones”.
Here’s the IP addresses I got from my provider just by reconnecting the VPN three times without even changing my virtual location:
It’s weird how eagerly people speaking completely out of their asses tend to double down when called out. Even if that would have been true, your original claim still would not work at all.