Yes, technically if the EU citizen remains outside the EU for the entire lifecycle of the data up to and including deletion, then it isn't covered. But if you store that data at all when they have returned to the EU, then you need to comply with the GDPR in terms of handling that data.

Also, as a UK citizen (formally EU citizen), I don't understand why US-based countries are so against the GDPR, as essentially it's just a codification of how to do the morally best thing for your customers. Any data you don't need for a business purpose should be deleted as soon as possible. You can have any data about someone as long as there is a justifiable business reason for it. You have to let someone know what data you have about them (if they request it via a SAR) and you have to give them the information up front to determine if they are happy with you handling their data, via a clear privacy policy and opt-in to having their data used.

Complying with the GDPR is pretty straight forward, as long as your intention isn't to profit by selling or otherwise making use of people's data in ways that they wouldn't be comfortable with. If you aren't doing anything bad with user's data and already following good security practices, including deleting data that's no longer needed, then you are already compliant with the intent of the GDPR and going from that to full compliance is probably only adding processes to be able to handle an SAR.