Just curiosity about procedures at Ho Chi Minh embassy

I have been asked for extra documents:

- Proof of being in vietnam, which i submitted already with the application, and i did add my flight and accommodation booking and payment

- email confirmation sent to the embassy from the muay thai school. (A 10 page document with all references was already submitted with the application)

- photos of all pages of my passport

Questions:

Is there any soecific reason about these requests of submission?

Does the embassy usually requests extra documents twice?

Thanks