In my place of work, something very similar nearly happened on one of our A320's.
The problem was that someone had one master switches in on position and mode selector in ignition start.
The pilot procedure is to just start the APU prior to close-up and push back. So the fuel pumps were on at this stage and all that was left was bleed air.
Luckily enough the pilot checked the Mode selector and master switches position before selecting bleed air.
Myself personnally i always now check the mode selector is in Norm and masters switches in off before i select bleed air on.
You just never know what way the cockpit was left.