Angry for some reason

There are so many variables I can think of that my dragon is mad. The story is I got new lights for my dragon and turned them on. I then walked away and came back and when I opened the enclosure my dragon after 30 seconds started to bob his head and beard turned black but mouth was closed. While this happened he was right below the screen so I thought that was a sign he wanted food, so I fed him and he ate it. At the time I didn’t know he was angry because he beard is still kinda black when he is calm. Then once I fed him I tried to hand feed him collard greens again and then he didn’t want to eat it so I left the room again. Once I came back he was running towards the glass. There was a reflection of him but it’s kinda weird he ran at it when I came in. Next thing you know I move and he runs towards the other side of the tank when I suddenly move but he was looking and ran at his own reflection. Is it me or his reflections or something I did wrong. He’s 2 1/2 and I got him from a breeder and he never usually gets mad at me until yesterday. He’s still new but when I first got him he seemed like he was really chill.

Edit: glass surfing was the problem. Is there anyway where i don’t have to spend money on a terrarium background?

Just use brown paper taped on the outside of back and sides