Is there always a bit of truth to a joke? boyfriend joked with me about something im insecure over?

So I have heard that there is always a little bit of truth to a joke that someone tells. Well the other day my boyfriend joked that my vagina was "loose." And tbh, it kinda hurt my feelings and he immediately rushed over to me and said it was just a joke and apologized. But why would he even joke about it unless he had been thinking it? I'm not fighting with him about it or anything, but it still kinda bothers me. Of he joked like this, could he actually think that about me?
Is there always a bit of truth to a joke? boyfriend joked with me about something im insecure over?
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