When you do business with a customer asking for the location is a common part of the sign up process.
We're talking about a law that is about data gathering, if you're not gathering data about that customer there's nothing to worry about.
It's much easier and safer to just assume someone who's in Europe is a resident, rather than figuring out if they really are.
GDPR only applies to EU residents, yes, but not if they're on ex. holiday outside of EU.
Say, a EU citizen is on holiday in The U.S.
In such case the EU citizen is not protected by GDPR.
While this is an interesting way to interpret it, it's likely that the law may be clarified in the future to state that if at the time of collecting their data the user is in the EU, the protections shall apply to said data regardless of where the user is now.