If it is Goldov, I can only guess his motivation is one similar to Adlet's village. While he was travelling, one of the major intelligent fiends approached him or completely overwhelmed him. He may have felt or was convinced that there was no way the heroes could defeat the Demon God this time, and made a deal to assist their plan if they promised to keep Bunny-hime safe and let him have her.

He may not have known all the details of the plan, only what he had to do as part of it.

Otherwise, it is probably Maura, tricked into it somehow. She came off as really stupid this episode. No wonder Chamot likes her, they're both mentally little kids, throwing tantrums all the time. She convinced herself that if it wasn't the most obvious one (Flamie), it had to be the next most obvious one, Adlet. Critical thinking skills aren't her forte.

This whole time the two of them have been manufacturing reasons to justify their choice, refusing to admit they're wrong a second time. The only difference is Chamot is a little more mentally mature and her tantrums are a little more obvious.