Tbh, it sounds like she did try her best to clarify by mentioning her boyfriend before they actually went to the destination.

She mentioned it pretty much last minute on the day they were supposed to go. We don’t know the full circumstances and I get that you’re trying to see it in the best light but the situation was far from optimal. Best moment to ask would’ve been before agreeing, so whether purposefully or just because she didn’t realize, that’s where her error happened. Not to say that the guy couldn’t have clarified it was a date.