It is weird. I wonder if there was some miscommunication initially and the other family wasn’t specifically inviting you on their trip, as much as saying if you made a parallel trip the kids could enjoy sone time together, which they did.
Generally, I think shared vacations are a terrible idea. Even with extended family who grew up with shared experiences, there are liable to be conflicts. Traveling with friends seems a quick way yo break a friendship.
I think in this case, give them the benefit of the doubt, chalk up the vacation fiasco to a misunderstanding, and socialize casually with them, as before. In the future, if ANYONE talks about going on a trip, wish them Bon Voyage and make independent plans for your family’s vacation.