You need to get tested. But the chances are quite slim that he is HIV positive, and even if he is, the chances are further slim that you would have got it from just this ten seconds of exposure. However, you did insert your penis into his anus and so you need to get tested. Do not panic, and do not Google for hiv symptoms. Just go and get tested. All the best.
Any penetration is a risk so you should test with a duo after 4 weeks or any other test after 3 months for a conclusive result. Just test once.
Anyone can get a cold so ignore what you think are symptoms and relax until your test since he claims to be negative.