Watching Alex Smith throw an interception is a rarity. Let's face it, with the exception of the last few weeks, Smith is normally known better as the league's best game manager, rather than an elite QB -- but don't tell Smith that.
This is simply a case of trusting your arm a little too much. Looking for Delanie Walker, it's just his second interception of the season, and Prince Amukamara took advantage of the under-thrown pass.
Is enjoying Smith's failure wrong? Probably. Look, he's the league's best passer by rating, so we can all enjoy our Schadenfreude.