If we accept that Guybrush was imagining effectively the whole game, it's not a stretch to think he might also have imagined the glowing eyes and Elaine's line on his way out of the park. I accept that the ending was likely intended to be taken literally, and that if there were a third game shortly after MI2 it likely would have elaborated on that and had Guybrush going in and out of the imaginary world. Could've been neat.
The only thing it leaves me wondering is that if "the secret of monkey island" was that Guybrush was just a kid playing, why would Ron pretend it hadn't been revealed when MI2 had effectively revealed that. So I think the titular secret may have been something else altogether.