@Dario *******
You are falling for a grand misunderstanding
When the Ho Chi Minh Thai consulate told you that you could apply for the METV even while being inside Vietnam, they didn’t make clear at least the basics!
You cannot apply for a METV in any other country but in your home country.
You can only apply for the single entry Tourist Visa in another country than your home country
But YES, you can apply while you are staying in Vietnam.
They, however, forgot to tell you that you could not apply at their consulate, but in the Online E-visa system of your home country, while you were staying in Vietnam.
That’s the misunderstanding around your personal experience
You didn’t even question this. And you didn’t try to apply through your home country’s E-visa system.
If you did, you would have found out that you probably were to prove that you depart by a flight from your home country.
Or worse, you would have found out that they found out that you weren’t in your home country physically, and reject the application
You should trust in the group admin’s knowledge.
Myself I have never found the admin wrong, in the many years I am a member in this group and reading in it every day