Why did I get blocked for this?

[lala]

Ok so I have Facebook but my friend doesn't and she sometimes uses mine to chat to people from uni etc. I didn't add this guy and I didn't know him, but I think she may have or accidentally added him.

He sends me a message which I only saw a month after cause fb put it in the "other" category.

It says "Who are you??? Just got fb, no mutual friends. Interesting!" Followed by another "hey do I know you or just random".

I saw it and I was like I didn't add him! So I write "omg I just saw this now cause fb put it in the junk category. I honestly do not remember adding you. I think I must have gone to add someone else.. sorry"

Then he blocks me! Wtf??? Why? Did I look like I wanted any further contact with him?

Sorry it's long. All advice is appreciated. Thank you!