SSOTN, I work in car insurance claims so feel qualified to give you some advice, but I don't think I'm going to bring good news.
How or where his car was parked isn't going to be a defence - it wouldn't matter if it was parked on double yellows either. It will be argued it was there to be seen. And admitting to a knock, however slight, will cause your insurers some concern and if they get to learn of this "accident" and will probably pay up - it's the cheapest and easiest option for them as it will be easier to say you did cause the damage than didn't. Another one settled and off their desk. Maybe a bit of a moan from you when they do, but that's an arguement you'll never win. Don't kid yourself that forensic engineers etc will get involved. They don't come cheap and if every bump like this had one involved we'd all be paying far more for our insurance. And the bump happening at night, probably in the dark, is also against you. How good a look at his car was it possible to take?
Difficult to say too much as I guess the bloke hasn't told you how much he is claiming for. Make sure any estimate is from a decent repairer rather than a back street job as they are far less likely to quote for damage that isn't there or was caused at another time. This leaves you open to a higher cost possibly, but at least you'll know that matey isn't profiting from this one.
See this an awful lot. You could think yourself lucky he wasn't sat in his car at the time, as no doubt they would claim their neck was hurting - then it gets really expensive. But I only see claims that do go as far as insurance - I'm sure loads are never followed up, or settled with a few quid. Hopefully that is what will happen with you. Good luck.