Tags in questions are ordered by frequency accourding to that post.
I noticed a question of mine does not follow that order (if frequency is equal to the number of followers of a tag).
If I am wrong: How to see the frequency of a tag?
The number of followers/subscribers is something different than the number of times the tag is used on a question. The latter is what determines the order of the tags.
The frequency of usage of the tags on that question is shown in the right sidebar: