I would have thought it means "apt to spill one's oatmeal onto his lap"
Interesting, how our experiences (and lack thereof) affect our understanding, isn't it? Having taken quite a few French classes, I recognized the name Pantagruel, and so never thought of the porridge angle. Let me hasten to say, however, that there are many more things here that I have no frame of reference for.

I will post again (it having been a long time since) that it fascinates me, how we immediately try to fit new experiences in with what we already know. I guess it started when we took our son to the zoo when he was just beginning to talk: the first animals we happened to come to were the goats; every new animal he saw thereafter, he'd yell "goat".