He was just doing his own things minding his own business while walking
He was walking till he found her Girlfriend.
Since they haven't kissed for A while, they decided to do so while not being seen or caught doing it.
After the kiss, he went and said goodbye to her since he's got to get home quick, she said goodbye back.
The End
Also when I was making this story, this was my reaction to it.
https://www.youtube.com/watch?v=dPXvMhwnf04
"WHHHYHYEYE DID I MAKE THIZ!!!" that's it goodbye.