Other mistake: During the shoot out on the train, Frank takes cover behind the seats. Needless to say, those seats would never offer any protection against a hail of bullets.
Other mistake: Near the end when the bad guy blows up in the train, the fireball created by the exploding bracelet would be much more suitable to several kilos of high explosive or a fuel explosion. It could never have been created by the amount of explosives stored in a bracelet (see as well Mythbusters, the James Bond episode with the exploding pen).
Other mistake: Franks Audi smashes through the steel barrier on the bridge. Whilst we can accept the bodywork is toughened up and is bulletproof, its a plastic front bumper, plastic grille, glass/plastic headlights, yet there isn't even a scratch on either of these items after the car is seen driving after its pulled from the river after smashing through said STEEL barrier. The barrier would be particularly strengthened to attempt to prevent such a maneuver that Frank performed.
Other mistake: When Frank's car lands on the moving train, it leaves no dents on the roof of the wagon at all.
Answer: Just before the scene ends, somone in black taps him on the shoulder and knocks him out. We can presume that the person in black is one of the bad guys.