How do you respond to an upset friend who goes through your Facebook account to confront you on events you’ve marked you’re interested?

Just sit down with your Friend Ask what's wrong and try and talk things out 

Go to his house out the back, sit down and open two cans of beer then calmly ask him to his face, "What's your problem?".

It's difficult to say, my young friend, as we don't know you or your friend, nor indeed, anything about either of you.  For instance you MAY be very young, so both of you MAY still be developing in maturity.  You MAY have very different outlooks on life.  You WILL have VERY DIFFERENT upbringings, etc.

I'm a fairly old guy (62) and am now sure of myself.  I've had a wide range of life experiences and I'm VERY confident.  I KNOW what I believe, and I KNOW what interests me.  I am NOT averse to arguing my points, though I AM willing to listen to 'alternative' viewpoints from whomever possesses those viewpoints, and I WILL try to understand where that person is 'coming from'.

If it were me that were in your situation, I would state that the interests are MINE and/or that I was seeking to LEARN from different viewpoints and trying to understand both the viewpoint(s) AND the person(s) expressing those views.

IF you friendship is strong, my young friend, you SHOULD be able to 'get over' any disagreements that you may have between yourselves.  I wish you well.