There was a Zeppelin in WW I that survive the explosion of a AA shell inside the ship. And that was filled with hydrogen. The crew was able to land it safely in the UK and had to destroy it with a flare gun. Those things are a lot more durable than you'd think, since the sheer volume of the lifting gas means you've got to tear the thing apart to make it fall out of the sky.
The reason they say it would survive a missile strike is most anti-aircraft missiles have very small warheads. An AMRAAM, for example, has either a 40 or 50 pound warhead, which is going to do less damage than an artillery shell. They only bring down airplanes because 1) airplanes are full of flammable fuel and 2) tiny changes to the shape of an airplane make it disastrously unflyable.