There is no way of knowing exactly how they have wired the pedestal without testing it to find out. If they have wired the 30 amp breaker off of the load side of the 50 amp breaker, then you are correct, it could start tripping the 50 amp breaker if both of you are drawing a high load. If they wired the 30 amp breaker independent of the 50 amp breaker, then there should be no problem. You could ask. Or wait and see. When you get there, you could turn on the 30 amp breaker with the 50 amp breaker turned off. If the 30 amp breaker has power, then it is independent of the 50. If the 30 amp does not have power unless you turn on the 50, the the 30 is a sub to the 50.
A 50 amp service is actually two hot legs of 50 amps on each leg, giving the capability of 100 amps total. It is exactly like house wiring in that it is a 220 vac split phase system with two 120 vac hot legs and a common neutral. However, unlike a house, your trailer only uses 120 vac even though 220 vac is there and available.
If they have wired the 30 amp breaker off of the 50 amp breaker, that would mean the other guy could be drawing a significant amount of power from one of your 50 amp hot legs and could lead to tripping. Even though there is theoretically 100 amps available, that is 50 amps each from the two hot legs running thru a 50 amp two pole circuit breaker. And you could have zero amps thru one pole and 60 amps thru the other pole, and it would cause the breaker to trip, even though the total was far less than 100 amps.
Bill & Patricia
2012 F350 SRW CC LB FX4 6.7