Why would he pretend to not remember me?

I texted this guy and he's ignored my texts before. Last night I texted him saying "hi" and he responded by saying "hi...who's this?" When I said who I was he ignored me. Why would he act like he doesn't remember my number when I texted him a couple of days ago and he ignored my text? That shows he does remember me. Does it have to do with the fact that I'm 17 and he's 25?
Why would he pretend to not remember me?
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