He was teasing Ridley as a boss to get people excited about Ridley as a boss, he doesn't troll anyone about things. He doesn't lie and he doesn't purposefully mislead. It was a tease of boss Ridley and that's all.
People can believe what they want but if that tease had been for anyone other than Ridley you would never see people react like this.
Why is Ridley handled so much differently than every other fan-favourite character then?
Why was there no "Just to confirm, Ridley appears as a stage boss" post that clearly states it quickly like with every other character?
"Other boss characters appear" means nothing because although a stage boss is a boss character, a boss character isn't necessarily a stage boss (see Bowser, Dedede, Bowser jr. these are all "boss characters").
It's ambiguous, and ambiguity goes against what he's go on record saying and it goes against his actions with every other character in the game. The only ones that have had any amount of teasing or ambiguity have ended up playable (Palutena, Dark Pit, G&W... Metaknight if you have the opinion that Georly mentioned earlier).