The filters themselves are sterile, obviously. Otherwise the oil would be touching the non-sterile outlet of the filter and getting contaminated again. So any filter fibers that are shed during the process are sterile as well.
Typically this is achieved either with high temperature or by exposing the filter to strong radiation, and then putting it into a sterile airtight package.
As far as 0.45 goes, it's not recommended but it's probably sufficient. Most pathogens will still get filtered out, there's only a small fraction that are less than 0.45, and a 0.45 filter still removes a good fraction of particles less than that.