What does it mean when a guy texts you out of the blue?

So last time I talked to him was last Wednesday and I asked why he's been really distant to me and different with me. (Previously, we ALWAYS talked and now he's distant and seems weirdly nervous sometimes). He told me a reason but it was kind of brief and I felt like he had more to say but he couldn't say it straight out. From then on, we haven't talked. I heard that he talked/asked about me with my friend and then out of the blue, last night, he texts me, "I will explain why I have been different to you, at school", followed by a kiss emoji. I told my friend and she said that this might mean mean he was thinking about me and he even remembers and thought about our conversation from 5 days ago.

What does it mean when a guy texts you out of the blue and says something like that? And the kiss emoji? Please help, I have no idea how to read this guy. Thanks.