Oxygen suggests plant life, at least.
The surface is exposed to immense levels of radiation, but the ocean is deep under the surface. Practically zero radiation gets down there.
No, oxygen doesn’t necessarily mean life. Oxygen is created on icy worlds by solar energy splitting water into hydrogen and oxygen. It’s at a very low rate, though. And who’s to say that Europa wasn’t created with oxygen-rich seas?
I don’t think there’s any way to say whether life was created elsewhere in the universe, but we need to be realistic about the evidence.