Other mistake: When Gerry and Segen are in the plane towards Cardiff, a zombie attacks a flight attendant and a whole section of the plane. Despite the fact that what's happening would be obvious to the passengers of that section, no one even tries to escape the attack by going to the back of the plane, in Gerry's section. Gerry and the passenger have the time to pile up luggage without anybody from the front section interfering.
Other mistake: As Gerry enters the aircraft carrier command centre, we see screens with "world projections" of remaining uninfected populations by continent. They are counting down (illustrating the quick spread of the disease). However, the countdown speed of all of them, is approximately 3% each second - which means humankind would have no more than 20 seconds at this rate. The countdown speed should realistically be about 100,000 times slower than that (about 3% each day), which would still be the fastest pandemic spread the world has ever seen.