PMBOK defines 10 knowledge areas, "that are typical of most projects, most of the time". Some Scrum processes/artifacts clearly fit corresponding knowledge areas. E.g. Daily Standup is an implementation of Communication management and Backlog grooming is part of Scope management.
Can one claim that Scrum is fully covered by PMBOK knowledge areas?
PMI itself has made this claim. I don't have exact citations right now, however as a PMP, PMI-ACP and a Certified Scrum Professional I've been in many conversations around how the PMBok can support agile.
Remember that PMBoK is a "Body of Knowledge". That's pretty much a fancy way of saying "Best Practices". The PMBoK is not a process or a methodology. It is designed to work with any project. Even today I lean on things I learned from the PMBoK in agile work I do.
