The Stryker that was destroyed yesterday burned because an external fuel can caught fire after the slat armor defeated the incoming RPG warhead.

A short CJTF7 press release sums it up:

A Task Force Olympia Stryker vehicle was attacked by rocket-propelled grenade fire in west Mosul this afternoon.

An RPG hit the external armor on the left rear of the Stryker. The armor caused the RPG to detonate before it hit the vehicle's hull; however, shrapnel ignited an external fuel can, causing the vehicle to catch fire.

The Stryker crew was able to exit the vehicle without injury.

Coalition Soldiers will continue to work together with Iraqi Security Forces to provide a safe and secure Iraq. The Coalition is committed to helping Iraq win this war against terrorism. These attacks show that those who are against progress are desperate. Terrorist acts only increase the resolve of the Iraqi Security Forces, Iraqi citizens, Iraqi Governing Council and the Coalition forces.

Remember the fire extinguishers? They must not have been able to get the blaze under control quickly enough. That's two Strykers lost to enemy fire. Both times the crew got out okay with minor injuries, but the vehicle was lost after a fire couldn't be put out. (via Stryker Brigade News)