Quite so!
It seems your average bird owner thinks it is clever to train birds such as parakeets, budgerigars, corellas, rosellas and especially galahs to say cute things like 'Polly want a cracker?'. The trouble is with galahs is that when they do talk they have an embarrassing habit of learning to say words said in many households which weren't meant for them to learn, eg swear words.
There was a newspaper article I read a few weeks ago, about some galahs and corellas, who had escaped captivity, then, having merged with the flocks of such birds in local parks etc, have been training other birds of their flock to talk. Are we going to go around censoring everything galahs in the wild have to say to each other and to humans?
We'd look proper galahs, that is to say, 'bird-brains', if we did that, now wouldn't we?
But since Eustace was seen talking to a seagull in the film, and was virtually called a 'bird-brain' by the likes of Rynelf and Tavros, we can't very well complain about any half swearword he might have been observed to have said.