I'm originally from Los Angeles. I've been eating tamales for over 50 years. I know what they are, I've even helped make them myself by hand on occasion. I've had them in the campos in rural central virginia.
In any tamal you have the cornmeal, you have the filling, you have the optional mole on top. This one was probably wrapped in a corn husk, cooked, taken out and cut.
Mabye not. Maybe it WAS a casserole. Same ingredients. YMMV.
There was of a pic of Carter eating through the husk of one during a stop Fort Worth in the 70's.