Why would a guy assume I’m sleeping around? Was it what I said?

I went to a party recently and my guy friend who I used to have a crush on (he’s definitely not my type anymore) asked me if I went with my boyfriend. But I’m single and told him “I don’t have a boyfriend, I’m single and just have friends I hang out with”. He told me not to sleep around with them and not to have a lot of guy friends. I asked him why would he assume I’m doing that, and why shouldn’t I have guy friend, and he left me on read. I suspected he liked me at some point but he’s in a situationship so my suspicions are probably not true. Other than that I don’t understand why he’d say something like that and leave it like that?
Why would a guy assume I’m sleeping around? Was it what I said?
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