That's a first-pitch curveball, a little out of the zone. Not only did Ichiro swing at it - Ichiro made contact, and obliterated the pitch into the right field stands. Said Hochevar:
"The first-pitch curveball to Ichiro, I don't even know what to say about that one," Hochevar said. "The [first pitch] of the game -- it was a good pitch and he hit it eight rows deep. I've never seen it, I've never had it happen. I normally don't throw first-pitch curveballs in a game, but what do you do?"
The entire sequence was incredibly rare. Going back to 2009, PITCHfx has identified 83 first pitches as curveballs, or 0.6%. Of those 83 first-pitch curveballs, batters have swung at just three of them. Of those three swings, two have resulted in fouls, and one has resulted in a home run - Ichiro's swing, last night.
I don't know if there's any greater meaning to this. I don't know if I have to look for it. My sense is that, no, I do not, because the event was sufficiently remarkable on its own. Last night, Luke Hochevar threw Ichiro a curveball with his first pitch of the game. It was a good curveball. Ichiro swung at it and hit a home run. Amazing.