Reddit should be able to tell by the number of different accounts that connect through an IP like that that it's not a home wifi network and treat it accordingly, the question is do they actually do that (probably cuz otherwise you'd never be able to connect through a VPN lol)
Either they’ll see it like some kind of public WiFi, or there’ll be collateral damage. But keep in mind that CG-NAT usually only applies to IPv4, so if your ISP and home network support IPv6, Reddit won’t have said problem and see you IPv6 address.
If that account only ever logged in there, maybe? I'd think they'd be smart enough to look at the most commonly used IP address by the account(s) in question. Then again, it is reddit.
I can’t say how they do it now, but it used to happen all of the time. A service would ban an IP that was shared, or even a range of IPs if the traffic was disruptive enough. Then the owner would have to contact the service to have their ban removed.
I’ve run into IP ban messages from both hotel WiFi and from VPN addresses.