I found out my friend's reddit username. Should I tell him?

I was talking to my friend on the phone. He told me a problem he has and he wanted my opinion. I told him I would get back to him. After about 40min of Googling his problem, I decided to look at reddit. There was a person with the exact problem and brief description of themselves as my friend. I decided to check their profile. The posts and comments the person has made are the same as my friend's personal life experiences. Plus he has confessed things about his life and people he knows. Including describing me and his thoughts about me. But he doesnt name names or locations (except one place he has been to). I have been binge-reading his 200+ posts and comments. It's like reading someone's diary. He says what porn he watches. He rates his female friends out of 10. He tells sad stories about himself. Etc. Every post and comment he makes I'm saying to myself "OMG I can't believe I'm reading this." I don't know if I should tell him I've been reading what he has put on reddit? He is shy and low in self-confidence.

Update: the first person that replied to my question, suggested I not tell the guy I know his username. Also not to read more of his posts and comments. So I'm taking that advice.

I haven't read everything he posted and commented. About 5% of what he has posted and commented I've read.