Anchoring etiquette

[Steel sails]

Anchoring etiquette
I understand last person in an anchorage has the burden to move if required. Last week chartering in Croatia, 50 ft Cat. I pulled into a cove behind a 35 ish foot monohull. 10 minutes later they were still motoring in circles looking for a spot to drop.
I only intended a lunch hook so chose a spot where they had turned away from, motored over and dropped the anchor in 15 m of water let out 50 m of chain and just a gentle back down.

Other boat comes back round and drops his anchor about 40 ft from ours, hands on hips like I stole his space. Luckily when he backed down he dragged about 100 ft before he realized it wasn't going to get a set on a rocky bottom like that. There was plenty of room and no need for him to come that close so I am sure it was in response to me dropping first.
My question who has the right? first person there or first to anchor.

Regards
Paul