Who was right in this situation?

bad question, we may have both been wrong, but what do you think? Me and my bf took a trip to monterey with my 4 year old. We had a plan, to meet his grandparents at the pier for an early dinner, then have just enough time to take her to the bay aquarium after. as we were driving, his grandma called and changed the plans, she wanted him to come to her house late for a bbq instead. he was afraid to tell her no. But, i made my kid a promise to take her to the aquarium, if we were to change the plans we wouldnt make it there. it seemed like he didnt want to change the plans but he did bc he didnt want to upset her. so i told him, im sorry but that was wrong, you need to get a backbone. i feel bad for saying that, but maybe its true. so now, i wont let him pay for everything, i pay for it, that way plans cant change like that. i mean, its ok sometimes to change plans, but when it comes to breaking promises to my kid, no way. would this kind of relationship work? im an independent say whats on my mind girl, hes a soft mamas type of boy....