No. You absolutely should not change the tag. Perhaps adding the tag would be helpful.
The purpose of the tagging system imo is not absolute correctness and a cataloguing of answers (this is not wikipedia.) The purpose of tags is so that answerers, readers, and askers can quickly and efficiently find relevant or interesting questions similar to those that they are thinking about.
In particular, this question might fit more naturally under the umbrella of differential geometry, but the OP's question is not really going deep into this, and neither are the answers, they don't use a complicated language to answer the question.
What would be helpful is adding a comment/answer mentioning that this is a special case of a metric tensor, and understanding this concept would help. Perhaps link a related question in the differential geometry tag. Now, you've directed other users that have not taken DG to a subject and place where the question more naturally sits.
For comparison, I think this is like retagging
- "how can I factor complicated polynomials?" with field theory or galois theory.
I just don't see who that may help except for those that already know the latter subjects.