Heathcliff, who will never hit a baseball again, has a perfect understanding of the English language. The ump is just being an asshole.
Also, that isn't what backstops look like. Or umpires. HE HAS NO EYES. He's also going to need some dental work if he bites on the bar that is very clearly in his mouth. Maybe he didn't say "meow," and was just mumbling through the bar, and Peter Gallagher had a hard time understanding him?