The comment was deleted because the system flagged the comment for low quality, it ended up going for review and getting deleted by a mod.
It shouldn't have been deleted as it answers the question, it does not fall into the categories listed below but things don't always function perfectly.
This is the recommendation from the stack exchange meta on low quality flagging:
There are several reasons for flagging answers as "very low quality".
They include, but are not limited to:
Severe formatting issues: If a post can be edited by a third party to improve it to the point of not meeting deletion criteria, you
should do so if you are able to. Otherwise, you can use the VLQ flag
to indicate that the post is not salvageable. A moderator will then
delete the post if it is of poor enough quality. They may also notify
the user of the reason for deletion, in hopes they may edit and flag
for undeletion.
Incomprehensibility: It may be an answer, but it's so bad that it could never be saved through editing.
Other severe content problems: This includes answers that don't attempt to answer the question (which can equivilently be flagged as
NAA) and answers devoid of content (such as "try jQuery!").
However, the "very low quality" flag should not be applied to an
answer if:
The answer is just incorrect. It is not the job of moderators to deal with answers that are incorrect in some respect. Users should
downvote wrong answers and (optionally) leave comments that describe
why they are wrong. The answerer would, in the best case, update the
answer to fix whatever issues it has, or delete it. We even have a
badge for that.
It is spam or abusive. Spam and abuse flags are handled differently and carry higher penalties. If a post meets the criteria for one of
these flags, you should flag it as such rather than Very Low Quality.
A "very low quality" flag on an answer that is technically incorrect
should be dismissed. The moderator may take into account the quality
of the answer when deciding to mark the flag as "helpful" or as
declined for one of the standard reasons.