What's the deal, when I text him he replies but then he unsent even though I have seen it and already replied to it?

Today, I sent Hi to my crush and he also sent back Hi. So I ask him if he knows me and that I am in the same class as him. He replied that he knows me and I asked if he had done the school work or hw, and he said "I haven't because I don't know" I replied to him with why you don't know with an emoji which is smiling face with a tear. after a few hours, I guess two or three, he saw my message and unsent the two texts he previously sent and left me on read. I am really confused and annoyed at the same time cause he literally left me on read.

What's the deal, when I text him he replies but then he unsent even though I have seen it and already replied to it?
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