Come on... Practically, the police can do whatever they want, and it's up to the victim to fight it in court if it was wrong. If an officer wants to detain you without reasonable suspicion, they're going to do it, regardless of whether it is legal. If they want to arrest you without probable cause, they are going to do it.

The OP said they were "detained", and then as evidence cited a story where they were not, in fact, detained.

That feels OK to point out.