Man catches wife of twenty years in bed with neighbour!

A man in my neighbourhood came home unexpectedly yesterday and caught his wife having sex with neighbour on their matrimonial bed!
He had suddenly run out of fuel on his way to work and discovered he forgotten his cash at home.
He picked a taxi home, ran upstairs and caught his wife doing the unforgivable with their neighbour.
The thing is he beat up his wife but left the neighbour alone.
My question: Is he not a coward? If he isn't then he shoukd have beat up his neighbour too.