The reason the comment is inserted first is because the comment is rolled up into the Case History Text field that is updated in step 2.
It would be preferrable to update the case first, so that if there are any validation errors on the Case, they occur before the comment is first inserted in order to prevent duplicate comments.
The Case update operation is executed before the Case Comment is inserted, so that validation or other errors do not result in extra comments being added to the case. (v3.33)