I thought about deleting the question, but decided to leave the link with brief summary as it could be useful for current and future users.
@DanBron's comment has the answer. According to How does editing work?,
If a comment has been added to the post since the previous revision by
anyone other than the editor, the five-minute grace period for editing will not be applied and the edit made after the comment will be shown as a separate revision history (even if it was made within the five-minute grace peirod).
I think two comments were added to the answer before the two edits were made (and later deleted). That's why the link shows the two revision histories even though the intervals are less than five minutes.
I started to find a duplicate in Meta Stack Exchange and found a question related with five-minute grace period in editing a question.
Reset question grace period once an answer has been posted.
According to Shog9's answer:
Edits will be rolled into the previous revision if the previous
revision was created by the same author and none of the following
conditions are present:
- The previous revision was created 5 minutes or more in the past
A comment has been added to the post since the previous revision by anyone other than the editor.
An answer has been added to the post since the previous revision
The previous revision was a rollback
The new revision is a rollback