Why did he like a bikini picture of me from ages ago?

So there’s this guy who I used to go to uni with but we never spoke. He was in the year above me and I got the impression he hated me.

So the other day he added me on Instagram, and he went back on my profile and liked a photo of me in a bikini from summer and it was posted four months ago. He also has a long-term girlfriend.

why did he go back on my page and ‘liked’ an old photo?
Why did he like a bikini picture of me from ages ago?
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