Umm ..
Normally when someone says this it's because they want to date others .

The bad part is it's one of his friends so I can see where you feel a bit guilty because it's someone he knows .
But bottom line is he was the one who ask for the break up so whatever happen between the times you broke up he has no control who you saw .

I would not say anything because if you do he will always wonder if you will go back to
him .