I'm skeptical of the claim that the inquiline behavior is something complex. The ant isn't literally aware of "I'm as social parasite and therefore do all these things". It's just behaving randomly.

Arguably, the complex behavior is, in fact, not laying eggs in other colonies, which the mutation breaks.

Scientists should be skeptical of a elaborate hypotheses like "a new, complex behavior has emerged via a single mutation", and look for the simplest possible interpretations of what is observed. Occam's Razor and all that. For any hypothesis, you have to look for reasons and ways it might be false.