The vehicle itself seems lightly armored, and while an airburst would have certainly done the job, i standard anti armor missile or rocket is the fastest way to respond to most threats. All this being a moot point considering this is a demonstration.
If I were to guess I would say that it's a shaped explosive that forges a disk of some soft metal into a plasma lance. It's a very cheap way to defeat armor.
I always loved tanks, fascinated by them but I would rather scrub potatoes for rest of my life, to drive one to combat- especially after seeing these effects of AT rounds.
Negative. The M1126 Stryker ICV does not utilize missiles for a weapon, but rather mounted and belt fed MG's like the M240C and M2 Browning. Also, our Strykers are nowhere near that sleek or pretty.
Source: I'm in the 3d Cavalry Regiment, U.S. Army, we use Strykers.
Pic: M1126 utilizing an M2 Browning while being clean as **** and missing some basic components required for operation.