Jonathan Lucroy is one of the best defensive catchers in the game. He's excellent at all of the underrated stuff, like blocking pitches, calling a game, framing his pitcher, and so on. He usually has a pretty decent arm, too, but you wouldn't know it by the way the bottom of the sixth inning started for the Brewers and Diamondbacks on Thursday.
Lucroy either looks away because he assumes this throw has gone as well as all of the thousands of others he's made in this very scenario, or because he knows, the second it left his hand, that he went and threw a mistake that looks straight out of little league. Considering he kept his head down afterward, you would have to assume it was the shame-based scenario.
It's okay, though. There was no one on base, so no damage done -- if you're going to temporarily forget how to make the most basic throw a catcher has to, that would be the time to do it.