MacBook Pro console system.log has weird user

You wrote "I have no idea what is Meos-iPhone device."

No references to it should appear on a Mac that you own, not unless you know and agree that phone has been authorized to that Mac.

I'm aware that Apple utilizes their devices for location tracking and other app-related activities. Is it the case?

Only if you agree to it: Change Privacy & Security settings on Mac - Apple Support. When setting up a new Mac, you are asked specific questions regarding that specific subject. Do you recall being asked?

You just bought it... from whom?

if the original owner did not perform this complex ritual, and deliver the computer to you running ONLY Setup Assistant, you probably need to go though this procedure yourself.

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

Apple software downloaded from the Mac App Store, including MacOS,  is not copy protected. However, it IS tagged with the Apple-ID of the purchaser when "purchased" (or equivalent. Think of MacOS as purchased on sale for $0.) A valid Apple-ID is required for almost all downloads from the Mac App Store.

You cannot update, upgrade, or install new software based on already-installed software UNLESS you supply the Apple-ID of the original software.