Well when a video is buffered it’s loaded in memory but not viewed yet, they can’t count loading the video as a view or they’d count the whole video as viewed if you simply buffered it in full, it would also screw up that watched timestamps feature to see which part has been played back most.
So yes they can count how many times it has been streamed but they also need to know you’ve watched it because sitting on pause while the video buffers all the way through isn’t a view, it isn’t watching those segments, but it does stream them from the servers, in the same way Newpipe and Grayjay does. Which is how a video can register no views despite being watched on something like NewPipe.