system
A chat on subreddit /r/me_irl
human
I'm no writing expert but how is the writing same? The 2s, 3s, 5s and *s look fairly different. 

Also she could've just used his pen to write down her number. 

Still probably fake but i don't think it's because of the reasons you said.
gpt
Watch the top of the notebook, there are the  c and 512  imprints of the napkin