E-mail counts as user identifying (it’s a bit more complicated) information per the GDPR, so clearly they have kept user identifying information so the GDPR applies.
EDIT: as pointed out by @coffeeClean and from reading recommendation wp136 provided by him in a different post, the e-mail, unless it contains the full user name is user idenfityable information - because it can be crossed with other data (not necessarilly the IP address) to identify a person - rather than identifying information. Either way, it is considered “personal data” by the GDPR, as said very explicitly in that document which gives e-mail as an example of such. The same applies to IP address (mentioned below).
Even an IP address is user identifying information per the GDPR, which is why if for example a website wants to be compliant without obtaining explicit user authorization, it needs to do things like not maintain logs with IP addresses for longer than it would be necessary to track down problems with the website or intrusion attempts.