It was vastly inappropriate yes, however a formal warning should have been given first.
Big Brother usually loses one person a week. This week, as a result of an internal email sent Tuesday morning from Ben Frow (the head of Channel 5) saying he wasn't happy with the current ratings or housemates, they are losing four. They are also, however, gaining four which means they are not losing one housemate overall as they usually do.
As a result, they were desperate for a reason to remove a housemate somewhere in the mix. They called Joel in, encouraged him to express his discomfort, then used this to remove Aaron in time for Friday's live show.