Hmmmm, when you were trying to nurse your plane back to the runway, were you at idle? If so, did it seem the engine would have the power to yank the plane as erratically as it did? The one missing clue of this being a loose engine is the erratic behavior being related to how much throttle you had. In other words, at a constant throttle, I would expect the behavior to remain somewhat constant, and then when you change throttle, the plane would change its behavior. A loose engine, however, can change its throttle on its own- did you hear the engine throttling up or down on its own?

And, yes, my first guess is radio. Did you immediately check battery levels and test the radio components?

In any case, I agree with Bruce in that you should ALWAYS immediately land a plane that shows any erratic signs. There is no reason to believe that the degree of erratic behavior will remain constant. I hope you can get your bird back in the air soon!