It looks like the pedal was crossthreaded when installed and instead of the mechanic owning up to his mistake and replacing the crank, he just used the long pedal wrench to force it in. This cut new threads in the aluminum crank alongside the original and weakened the holding force of the crank. Repeated pressure on the pedal caused the axle to pull through the weakened threads.

Assuming these are the original pedals installed by the LBS where you bought the bike, you have a beef with them. Since you stated the bike is brand new, there should be no question of warrantee repair. If you installed these pedals yourself, the issue gets a bit dicey.

For the benefit of the home mechanic: It's very easy to crossthread a steel bolt into aluminum. The aluminum is softer than steel so it's easily possible to get a half turn or more with the bolt before you realize it's crossthreaded. Whenever possible, one should always turn a bolt backwards until you feel the threads 'click' into place, then turn forward to engage the threads. Turn gently and if there is any binding, back the bolt out and check for crossthreading.