I don't believe I did anything wrong.
The warn for prop surfing was definitely acceptable as he admitted it right in front of me. If you did not see the screenshot at 2:34, he has placed a prop in the mines, and was clearly surfing on it. This along with his confession to prop surfing is enough to warn him for prop surfing.
Now, to explain the warn for building in mines. I consider building as placing any prop down, no matter if it is 1 prop, or 50 props, whether if it's a structure, a base, or a cube, I will still consider that you're building. I think we might all have our own opinions on whether or not you would consider this "building" but, at the end of the day, he still placed a prop in the mines. And what happens if you put these two together? Building in the mines along with prop surfing.
Now.. if this had happened in the street, I would of only warned for prop surfing. I'm sorry if I was a bit harsh, but I'm strict on building in the mines (with the exception of text signs).
I hope I have explained myself well enough.