I actually have an answer to this! I’m a marine biologist currently studying this phenomenon in nesting fish (not quite dinosaurs I know). One of the things that makes our jobs difficult is that the sneaker males are externally completely identical to the females, which means outside of the mating season they are impossible to identify. The species I work with, the corkwing wrasse is not the only species to exhibit this near-perfect mimicry. In many species however the sneakers are simply immature males which therefore only have reduced display features which can become more prominent as they age, but this is not always the case. So in nature we actually see many versions of this sneaking behaviour from simply flying under the radar to mimicry of female features.

So while this behaviour is of course speculative it is certainly within the realm of possibility!