Is there any other natural expression in this situation?

This was my conversation with my friend today:



"Hey, you study so hard nowadays.

Whenever I went to the library, I saw you in the same desk"


"No....it was that I was just coincidently there when you came to there,

I studied only 1 hour per a day"

You could say any of the following:

"It was probably a coincidence, since I was only there for an hour each day."

"It was probably by chance, since I was only there for an hour."

*I don't often hear people use coincidental/coincidently in everyday conversation.  I hear 'by chance' quite often in the US, but I'm not sure about New Zealand!

If you want to be funny you could say:

"Are you trying to hide the fact that you are secretly stalking me? "

"Are you following me?"