The specific case has been explained in the comments, but let me remark on comment deletion in general.
I am a regular user on this site and a moderator on another SE site.
Comments are second class content on all SE sites.
A comment can recommend clarification or other edits, and the comment is obsolete once the post has been edited accordingly.
If the OP does not respond to the comment, you can consider making the relevant edit yourself — within reason.
Answers, no matter how simple, should be posted as answers, not comments.
Do not put anything valuable in comments.
Valuable content belongs in questions and answers.
Comments are transient notes that are supposed to help improve questions and answers.
The threshold for deleting comments is low, and this is on purpose; they are a sidetrack to the actual Q&A activity.
Admittedly, there are insightful or otherwise useful comments that one might prefer to keep.
But even then, it would typically be better to incorporate the comment into the commented post (with proper attribution) and have the comment deleted.