Hi Debbie
In my experience some breeds do seem a bit more prone to things like mouting and humping, many of the ones i have seen are labradors. But that doesn't mean it is always these breeds.
Some dogs just develop the behaviour if it has been accidentally reinforced eg people laughing the first time it happens. This praises the dog and the problem can start from there.
Other dogs just start it for no particular reason.
Whatever the reason reprimanding it is the best way to fix it
Todd