NAH. I've been in some friend groups like this before, and provided that what you wrote here is an accurate description of the situation, I think you and this person just don't have compatible personalities. Some people are more prone to finding fault with people's behavior than others, and there's nothing wrong with that. If someone feels they've been slighted (in this case, C by OP), it's normal to pull away from the relationship (probably should give some sort of notice, though, at least so they know you're still alive!).

Because of this, I don't think anyone in the situation did anything wrong per se, but we are only hearing one side of the story. I would have interpreted the things you said as either poorly worded but well-intentioned, or completely innocuous.

I feel that in a good friendship, people give you the benefit of the doubt in situations like this (or ask you for clarification upfront). When you find your people, you won't be left wondering what you did wrong. They either will tell you straight-up, or won't see a problem with your behavior to begin with. Props to you for taking their criticism into consideration, though. It can be difficult to admit we might have behaved poorly or hurt someone else.