I think she thought you took “Adventure Buddies” as FWB, and then when you tried to explain yourself she saw it as backpeddling. Weird to use a term like that, I would usually call them “friends”. Anyway escalation, escalation, then over.
I get what you were trying to say, but it did come off as a bit oversexual. You didn’t mean it, don’t beat yourself up over it, just take it as a learning experience. Saying something outright like “FWB” to me comes off as “They have sex on the mind.” Rewording it to “I get it, I’ve tried the more casual thing and I think I’m looking for something more serious. Sounds like you aren’t, I get it, I’ve been through the same. If you do become ready, I’m always happy to meet for coffee”. And that’s it, no more follow ups, that’s the end of the conversation.
She isn’t innocent either, but I think she had her guard up and so she was in a mindset of taking things negatively. Just next time with the next person just keep it light, chill. Understanding, but yeah steer away anything that might come off as you’re trying to get in their pants. HR’s favorite phrase is “Intent is Irrelevant”, if they took it that way, then you probably should reflect on why they took it that way.
Last thing, the last message is very passive aggressive, and I know you were mad, but phrases like “You are” and “I’m sorry you feel that way” are very confrontational. A better closing would have been a simple “I’m sorry, I think we had a miscommunication, I apologize if what I said came out wrong.” “I’m sorry”, “I think”, “I apologize” instead of you