04 Grand Am won't start after clearing a P0455 code, coincidence?

Question

04 Pontiac Grand Am "Service Engine Soon" light came on. I borrowed a OBD2 scanner connected to a smart phone app and determined that the only code was the P0455 Evaporative Emission Control System Leak Detected Gross Leak. I read the code with the engine running, jumped out, checked the fuel cap which seemed a little loose so I retightened it jumped back in and hit the clear codes button on my phone app. Light goes off and I drive a few blocks to the hardware store. As I'm leaving the store, I try to start the car as normal. It fires up briefly and dies immediately. After cranking several times with no fire, I go back into the store, buy a wrench and disconnect the battery. I let it sit for a few seconds, reconnect and try again with no better result. I sit there for a while testing it periodically with no luck. A couple times it did fire but not even all cylinders, like maybe just one or two, more of a cough than a fire. Got a friend to drag me the few blocks home and now the car is sitting in the driveway with the battery disconnected. Will try again after work but not optimistic about any changed results. I will also check for spark and attempt to check fuel pressure if/when the engine still won't run.
Questions: 1) Could the short drive and stopping right after clearing a code have somehow confused the ECM causing the failure to run? If so, how do I get it "unconfused"? 2) Could the P0455 code have been a symptom of a bigger problem that didn't show up on my code reading app? I'm thinking maybe fuel pump failure? 3) Is this a complete coincidence and the code question just has me barking up the wrong tree? 4) Has anyone heard of a car being killed by running one of these OBD2 Bluetooth scanners?