Note that there's no such thing as "US IPs". GeoIP works by induction: "OK, this operator is in France, so all addresses in this range are probably in France; these ones are probably close to Paris, which is where this internal router is;" etc.
If I had to guess, you probably get the address of the base station whose signals reflect off the satellite, which is probably not very far from you, given the satellites are in LEO.
EDIT: I meant to say that you get an address in the ground station's subnetwork. I don't know if Starlink uses NAT.
GeoIP works by many different means. There are many different GeoIP databases which contain different data based on different opinions. Some are voluntarily reported, some by ping timings, some based on the registered address of the owner of the block of IPs, some based on business records, some based on third party reporting of other direct measurements, etc.
Sure there are. IP addresses assigned to an organization with a US address (typically by ARIN) are US IPs. Of course, there's nothing that requires those IPs to be used exclusively for destinations inside the US.
I hadnt even considered that there were multiple ground stations. I just assumed the Starlink satelites would just all bounce the signal back to base in the US.
Also, people in Europe don't want to have to take a round trip to space via America just to pull up IKEA's website hosted next door. That's a lot of pointless latency when you could bounce it down to a nearby ground station instead.
If I had to guess, you probably get the address of the base station whose signals reflect off the satellite, which is probably not very far from you, given the satellites are in LEO.
EDIT: I meant to say that you get an address in the ground station's subnetwork. I don't know if Starlink uses NAT.