this is his own estimate, based on his mates and what claptrap they spout when they are showing off to each other in the pub, so should be taken with a pinch of salt.
most of the tales he will have heard from guys will be just that - tales.
we all know that most blokes make this stuff up all the time, but for some reason some other blokes will fall for it - even though they themselves make stuff up too - many don't seem to realise that if their own stories are largely false it is likely that all they mates stories are too.
90% is just wishful thinking - it is the amount that would like to cheat given half a chance