Yesterday (2024-05-02) at night I saw a SpaceX rocket from my home in Lithuania (Europe) for the second time in my life. It was Falcon 9 second stage carrying two "Maxar" satellites launched from Vandenberg Space Force Base. It looked like a small galaxy slowly moving across the northern part of the sky.
But I couldn't find an answer as to why it was visible thousands of kilometers away in Europe. I follow some telegram channels and people over in Ukraine also noticed it.
Although you probably did see Falcon 9 it would not have been the launch itself but more likely the second stage deorbit burn which occurred after the Maxar WorldView Legion satellites were deployed. That's a hard thing to confirm with limited information, but I will go through some evidence that this is what you probably saw.
First of all your intuition is correct that you are not able to see Falcon 9 launches from Europe. For example when Falcon 9 launches from Cape Canaveral, SECO (second stage engine cut-off) occurs while the rocket is still over the Atlantic Ocean and still much closer to the U.S. than to Europe. This is when the launch vehicle and its payload reaches orbit, or at least an initial orbit. When launching from Vandenberg, SECO occurs over the Pacific Ocean even farther from Europe.
The SpaceX livestream for the WorldView Legion launch did not display a ground track like they often do, but this map of the exclusion zone for the launch indicates the direction that the rocket traveled as it left Vandenberg:
A SpaceX graphic from the webcast of the recent USSF-62 launch from Vandenberg on April 11, 2024 with a similar trajectory shows an example of where SECO occurs. As you can see it is still relatively close to the U.S. when it reaches orbit:
USSF-62 trajectory (SpaceX)
However whereas the initial launch to orbit can only be seen from a few hundred kilometers from the launch site, on-orbit burns including deorbit burns can be seen from any location in the world where they happen to take place.
Ground tracks for short-lived second stages are not usually available, or at least not easily obtained, however we can look at the ground track for the WorldView Legion satellites after their release and see that in fact they passed nearly directly over Vilnius at 10:55 pm local time (EEST) which was 80 minutes after the liftoff from Vandenberg.
WorldView Legion ground track (Heavens Above)
You didn't mention a time, but is this about when you saw the "slowly moving small galaxy"? If so there was a video posted by someone in Poland at nearly exactly the same time (9:55 pm CEST) showing the Falcon 9 second stage deorbit burn:
The video is a time lapse so it appears to be moving faster in the video than it actually appeared. If this is similar to what you saw, and if you saw it at this time, then it's almost certain that the slow moving glowing cloud that you saw was the Falcon 9 second stage deorbit burn.
When a satellite is launched, it goes into an orbit, generally a circle or an ellipse. That orbit is centered on earth's center of gravity. One point on that orbit has to be fairly close to the launch site. It looks like another point of orbit is visible from your location. Or maybe you saw the satellites on their next orbit (~90 minutes later, so the orbit track moves 1500 km to the West compared to a point on the equator).
So you weren't seeing satellites thousands of km away, they were more or less directly overhead.
The date indicates we're looking at the first WorldView Legion launch.
Successful launch 2 May 2024 at 18:30 UTC (11:36 am PDT) from SLC-4E at Vandenberg. First two Legion satellites delivered to 520-km, 97.6deg SSO with 10:30 LTDN. Falcon 9 first stage 1061-20 landed at LZ-4.
So they were launched into a sun-synchronous orbit from Vandenberg (coordinates 34.7431/-120.5144).
You're in Lithuania, around 55N/23° E. I think you saw the satellites after a few orbits. The first orbit would put them over ~60° E.
