A possibility here is that the seller simply didn't send you the bitcoin immediately, hence it took a good number of hours.
another possibility that i have recently encountered myself is that they (usually some services which may have been the withdrawing source of the person sending coins here) create a chain of unconfirmed transactions by spending the output of their previous tx without waiting for it to confirm and they pay low fees so they all take a very long time to confirm if there is a slight increase in fees (like from 1 s/b to 2 s/b)