My friend had ICE Wall of Thorns up in front of his HQ (I had forced him to Rez it previously with an event card)

I had Corroder Installed and made a run

I had 4 credits left.

Initiate Run 1 click (im now out)

Boost Corroder to 5 : 3 credits

1 credit to break Sub Routine of my choice on Wall of Thorns. I picked End Run so I could keep going past it.

I suffered the 2 net damage since I could not break that other sub routine and discarded 2 cards randomly

I hit his HQ and I RANDOMLY? Picked a card from his hand. It was a Operation with no Trash cost. So I had to leave it. So basically I made the run for nothing

Seems like you did everything correctly

Yep. Unfortunate not to hit a card you could steal, but that's how it goes. Can't find any rules-error in what you described though.

Yup. If a card has no trash cost then you can't trash it (unless you have a card that says otherwise like Imp). It's just the way it goes sometimes I'm afraid.