Minor bump into a hire car

This day I rolled very gently into the back of someone's hire car at the roundabout.
There is no visable damage to either cars but as the guys car is a hire car he wants to report it to them.
Do hire cars check 'internal' damage after every hire ? I'm worried they will say I've caused lots of internal non visable damage and make me pay when actually how can they prove it was my doing at such a slow impact.
The guy said if it wasn't a hire car he wouldn't of even stopped me as there is no damage but I'm really worried now