I don't think this professor is exceptional, but rather the norm. As a PhD student in computer science I regularly observed people publishing papers overlapped

I don't think this professor is exceptional, but rather the norm. As a PhD student in computer science I regularly observed people publishing papers overlapped to 80% with their previous paper. The difference being that paper 1 was titled "Solving problem X using Y" whereas the next one would be "A Y' approach to solving the X problem"