Well, is your check engine light on? If not, then it was a "soft" code that reset automatically. The computer will store the codes though. You can reset it with the Scanguage ya know.
All kinds of things will set off codes- when I was at Duc's shop the first time, he programmed some options for me with his techstream software ( windows down with remote, etc.) I had about 5 or 6 codes stored ranging from failure to start ( I released the key before it started) to others due to running the truck with various connectors un-attached (MODS, my friend, MODS).
During your various underhood installs, the MAF plug may have been disconnected to move some wiring around, and the truck started briefly with it unplugged, for instance. Code stored.
In short- reset it with the Scanguage. If the Check Engine Light does not light and the code does not show up again, consider it just a tattle-tale computer code, nothing more.
Make sense now??