The team is opting for stealth, yet have unsuppressed weapons. It is standard procedure for any special operations team to use unsuppressed weapons when on a mission requiring stealth.
Captain Amy Jennings uses a flare gun to ignite a bundle of C4 explosive when the igniter failed (furthermore, the igniter was flaming, which does not happen for standard C4 igniters). C4 cannot be ignited by incendiary objects; only a blasting cap can ignite C4.
A car explodes after being hit by a machine gun. Cars simply do not explode; petrol is a stable fuel.