Why would someone lie about not having an instagram account?

So I've been dating someone for a while now, more specifically for the past nine months. When we first met I asked him if he had an instagram account and he said no. Yesterday out of nowhere I found his instagram account which is private and I cannot understand why would someone lie about this. He doesn't seem very active since he only has a few posts but I cannot see what type of content he posts because it's a private account.
Why would someone lie about not having an instagram account?
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