But aren't all confirmed characters also trophies? I see what you mean but I just look at it differently.
We'll have to agree to disagree
Welcome to the forums, haha! Note that there are a lot of people who come to "troll" the thread, and they're generally quite rude, so tensions tend to run high pretty quick. Don't take it too personally.
Historically speaking, being revealed as a trophy FIRST essentially deconfirms a character. This is because every character reveal is meant to be exciting and dramatic, and trophies are never a good "first reveal". Yes, every character has a trophy, several if they're playable, but if the trophy is shown first there's a very very very good chance that the trophy is the only representation that character otherwise has. Like for example, Waluigi is an assist trophy, but we saw in game footage of him, and we have yet to see any trophies of the playable characters we have. If we do, we see the trophy looooong after that character has been fully revealed and confirmed.
As for why Ridley has a chance, there are hundreds of pages of discussion but I'll shorten it as best I can.
1) The size of the shadow. There've been quite a few analyses of the shadow's size, you might be able to find them if you're curious, but basically the end result is that Ridley has been resized from his Brawl counterpart. He's dramatically smaller, and we're not exactly sure why. I mean, if he is just a boss or a stage hazard, why would you bother attempting to make him smaller? It's odd.
2) The behaviour of the shadow. It moves jerkily and suddenly. If you look at footage from Brawl, or any other boss character, their movements are telegraphed and very smoothly animated. Only playable characters (that we know of) move in such a sudden way.
3) Sakurai's willingness to deconfirm. This go around, Sakurai has been trying to make things as clear as possible. He'll explicitly say things like "Unfortunately this means that _____ won't be joining the roster". Even in the Lucina reveal, he made sure to highlight the fact that Chrom is not playable, but exists in Robin's final smash. When he reveals people, he really reveals them. But before that time, he won't even so much as acknowledge their presence. Because Ridley has been teased so much, but never explicitly mentioned, people are wondering what it means. Sure, it doesn't necessarily mean he's playable, but it does mean that Sakurai has something in mind for him.
4) Metroid is an important franchise, and it needs more representation. The simple fact of the matter is that no other character fits as Metroid representation, really. Hell, they had to resize Ridley to make him fit, theoretically, haha.
So yeah, there's loooooads more, but that should be enough to ease you in! Hopefully you see our side. Doesn't mean you have to agree with it, so don't feel pressured. Enjoy your stay!