[lewiseason]

What GDPR says about this is:

> [A]n identifiable natural person is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person.

I think the principle is that since an IP address could be used to identify you, it is considered personal data.