A friend of mine didn't understand how he could have done better than me in a "write a quick sort" interview (we were still students) when I knew the algo and he never heard of it (and obviously struggled more).

Well, in one case (me), all the information the interviewer had was "this guy happens to know how to implement a quick sort by heart. K.".

In the other case (my friend), he got "this guy is able to understand and implement an algo he never saw before in a reasonable time", which is much more impressive