I do agree with your suspicions. They're the same reason I always find Yiga scummy, even when he's town. This time is no different (meaning I do get scum vibes from it), but the fact that he seems to have some small sort of reasoning that only makes sense to him seems to have a little bit of his town play in it. Even if I don't agree with his reasoning, usually when he's town and doing something scummy, it's because he has some idea behind it.
True, Ryu hasn't been scum yet. He's played a pretty strong town game in his other games so far. That's why I'm suspicious of him this time. Usually he has a lot to say, but this time when he was called out, he didn't even have any defense besides claiming and voting the second highest wagon. Just feels a bit like he got caught early his first time as scum and isn't sure how to react. I'm not sure if he was trying to claim Vanilla townie or just saying he's town in general (which everyone would say). But claiming Vanilla is an easy scum claim as well. Plus, jumping on the Jamie wagon doesn't look the greatest. Sure I get wanting to save yourself, but if you're town you should still be trying to scumhunt even if you're in a tough spot. If Jamie's town, and a power town role at that, than Ryu may have saved himself but gotten an useful townie killed instead. Pretty counter-productive to town's agenda.
My strongest suspicion still stays on Ryu, though I get what you're saying about Yiga. I just figure he's usually an easy lynch, so if he's scum we can lynch him just as easily tomorrow. Especially if the cop or seer checks him and finds out for sure.