Seeking sexual release is normal healthy human behaviour. Being "caught" implies wrongdoing. This is a hot guy being disturbed at climax. He has a wonderful healthy attitude, finding the intrusion funny & continuing to stroke & enjoy his orgasm, instead of trying to cover up the fact that he is enjoying an activity everyone engages in. The only acceptable actions when you interrupt someone performing a sex act are to apologise & quickly leave, to tell them how hot they are, to ask if you can watch or to ask if you can join in.