You conveniently avoid the fact that SpaceX inserted itself into a collision course with the ESA’s orbit, long after ESA had been there. Being that ESA has a “right of way” they asked SpaceX to take the action
The risk of a crash was 1 in 1,000. This is 10 times the threshold of 1 in 10,000 that requires a maneuver. Both of these satellites have been in orbit long enough for accumulated error to cause the satellite to drift from its predicted path. There are many satellite orbit-crossing events every day, and the accumulated drift is the primary cause of their orbits becoming close enough to require action. An anticipated collision that requires course correction is as close to a no-fault scenario as there can be.
ESA's orbit is itself constantly changing. Orbits are not fixed. They move constantly from orbital perturbation from Earth's gravity field, the moon's gravity field and, notably at these low altitudes, atmospheric drag. Again, who moved into who's path is not something you're going to determine. Yes SpaceX was lowering its orbit, but it's crossing hundreds of satellites paths by doing that, and even the orbit SpaceX satellites are in are shared by many other satellites. LEO is crowded.