The man didn't think of it should also be acceptable because the verb can mean both remember and think i am a native Irish speaker and our language has many verbs with double meanings. ex. Téigh can mean to go or to heat, so you really have to be careful.
The phrasal verb cuimhnigh ar can mean “think” in the “imagine” sense, or any of the phrasal verbs “think about”, “think of”, “think over”, or “think up”. (The object “it” could be used with any of them, but “him” could only be used with some of them.) Be sure to report this as an error when opportunity allows, so that these alternative answers will also become accepted.