Oh, I just don't know
Maybe that is the most likely explanation. I just wish I could be a fly on the wall sometimes without having to rely on second-hand accounts.
Having said that, given it is Falluja, I watched one American officer giving a speech to his troops just before they attacked - something along the lines of "Satan waits for you behind those walls, we're gonna kick his ass". Sorry, it's horribly paraphrased, but it was definitely 'Satan' and how they were going to kill him - these troops were getting fired up by all this religious nonsense so maybe it's not inconceivable.
The attitude that 'well we told civilians to leave so whoevers left is a terrorist' was a ridiculous one too. Picture how many American's would have refused to leave their homes if the Soviets have invaded: "I was born here, I grew up here, I'm not leaving my house for no-one" - its a perfectly natural reaction.