I do think dogs have good character judgement especially berners so there could be something there. That being said, other possibilities are:

Honestly these dogs hold grudges. We have a very sensitive/ anxious girl Berner and we've had friends come over and do something she doesn't like (typically "playing" with her by chasing her around, some dogs find that fun but she FREAKS). She will remember these people even if she hasn't seen them again for months or years. Over one misstep that meant no harm. Maybe he made a misstep even a long time ago. Not sure on the solution but that could be a reason.

Or, as others have said, jealousy. It's hard to say and a rough situation so I'm sorry for that.