Harry Z had a strong training camp and stuck around until the very end of the preseason before returning to the Adirondack Phantoms. He was a bit of a loose cannon out there, but he definitely has a ton of speed and isn't afraid to mix it up physically.
But why the call up? The Flyers already have 13 forwards on the roster, plus Ian Laperriere and Blair Betts on LTIR. We're going to have to assume that something else is going on here, likely an injury to one of the 12 forwards currently in the lineup. So, somebody not named Jody Shelley. That's what we're going with until we hear otherwise, at least. UPDATE: Reports say it's a minor injury to Andreas Nodl. So there you go.
As for why Zolnierczyk was called up instead of another player -- you're probably thinking Brayden Schenn -- it's definitely all about the salary cap. Zolnierczyk only makes $900,000 under the cap when in the NHL, and thus the Flyers can afford him right now.