Coming upon the scene as a detective (or an observer), one would suppose that it was purposeful (that he got locked in the safe). Because there is no other viable explanation of how it happened. (When Abigail later provides an explanation to consider, it is quite weak -- and she mixes it with her explaining to Columbo that she called Addie to turn the alarm back on because she forgot; a certain eyebrow raiser, especially given that she earlier plead confusion when Columbo put the question about the alarm to her and he said, "Oh, I can't really imagine you confused, Miss Mitchell."

Sharing the information (that it is not deemed an accident [because it very much looks purposeful]) with anyone is not only not a problem, it is valuable in rapid establishment of the case AND it is simply a conveyance of the situation as it very much appears. Here it may be considered the second move of this chess game; Abigail's mention of it as an accident being the first. Her forthright attempt to cast it as an accident is immediately met by Columbo's reply, which, reactionary, calculated, or otherwise, seizes the initiative. Abigail is thrown for a loss here, from which she never recovers and only slides in deeper, as evidenced in the conversation about the alarm switch and the later disclosure of her calling in to get the switch switched.