We've made some improvements to the automatic "trivial answer converted to comment" functionality to make it less likely that y'all will be confused by low-reputation users being able to post comments. Because conversion from answer to comment in this case occurred before the answer was created, there was no post history event to show the source of the comment, and no deleted answer.
From now on, when a comment has been created due to being converted from an answer, the field next to the comment icon will show the text "converted from answer". While we can't backfill this, it will be visible on all future cases where trivial answers are converted to a comment.
Here are the mod-converted and system-converted history events in a screenshot so you can see what the new text looks like. You can tell them apart because the mod-converted to comment will be paired with a deleted answer, while the system-converted will have only the comment itself.
In addition to this, we also updated the warning message for the poster so they are more likely to realize what happened to their answer when it got converted to a comment by the system. This links to the deleted answers help page, which we'll be updating with a brief explanation of what happens when an answer is converted to a comment.
I know that I've been confused when these automatic conversions happen and we've run into mods who are, too, so we hope this improvement will clarify things for people going forward!