He read my message straight away but didn't reply?

this guy wasn't online for hours and i sent him a message and he came online and read it within a few minutes but then just didn't respond. IS that because he didn't know what to reply and was awkward (this is a shy guy im talking about) or was it beacuse he wasn't interested? I thought because he read my message straight away (within a few minutes of sending it) it would imply interest?
He read my message straight away but didn't reply?
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