What did I do wrong anchoring in this scenario?

So this happened a few months ago and I have been trying to figure out what I did wrong. We approached an anchorage that is made by a man made artificial island in a crescent shape (Redfish Island in Galveston Bay) and wanted to anchor. There was already a boat anchored there, a larger vessel than ours and he was at a very leeward position in the anchorage. As I recalled from my training the correct thing to do was go far upwind of him to clear his possible swing area. He was far enough leeward that trying to go astern of him would have put us aground. So we went to the opposite side of the anchorage and dropped anchor and backed down. The dude starting yelling at us. He motored forward and pulled anchor than pulled alongside and said he was having to move because of what we did. We apologized and said sorry, we're new and still training. He said he wasnt mad at us but reiterated that he was moving because of us. He left the anchorage and we didnt see him again. I drew a picture to illustrate the situation and to this day do not understand how I upset him so much. What did I do wrong? There was no room leeward of him, we were a healthy distance a beam and I was having to guess his anchor location but seemed we all had plenty of swing room.

First edit:The only thing I can think of is we would have swung across his anchor rode, since I didnt know where his anchor was but almost no matter what with his position that seemed likely. But shouldnt his rode have been along the bottom, and being a larger vessel it was probably chain as well whereas mine was line with 10 ft chain splice. Shouldnt that have been fine?

Second edit: Ive anchored in this anchorage many times. Many times with other boats and followed the general guidelines I was taught. I remember my first time anchoring for my first overnight was an almost identical situation with two other boats, also larger than mine, leeward of me. And I got no complaints, that I knew of at least, those times. So I just really dont know what I did that pissed this guy off and now he has me questioning everything I know about anchoring etiquette.

Anyways, its been bothering me and I really want to know so I can avoid it in the future.

https://imgur.com/a/1eAQmzv