"Be going to" is Future Simple?

I passed a TEFL certificate test, and there was a sentence:

"We are going to stay with our family in Aberdeen."

And I had to choose whether it was "Future SIMPLE with "going to"" or "Present Continuous used as a future form", I chose the latter, as it was the closest ( the best answer would have been ""be going to" as a future tense/form (not SIMPLE)". And it says this is the wrong answer. The comment I got from them is this:

am/are/is + going + infinitive of main verb

(NB: 'I am going to Paris' is present continuous as a future form with 'going' used as the main verb; it's not future simple with 'going to' as long as 'Paris' is not a verb).

It's not Future Simple, Future simple is about will and shall. There's a reason we call all those tenses "Simple", isn't there?

Solution 1:

I am going to Paris' is present continuous as a future form with 'going' used as the main verb; it's not future simple with 'going to' as long as 'Paris' is not a verb).

This seems like gobbledegook to me. The more I read it, the less it makes sense.

My take on this

"I am going to Paris" can either A. be present continuous or B. it can be a prediction (there is no formal future tense in English).

A.

Police officer: Where are you going? (request to know your current activity)

You: I am going to Paris. (describing your current activity in the present)

B.

Friend: Where are you going for Summer next year? (request for future plans)

You: I am going to Paris. (prediction of your future activities)

Answer

"We are going to stay with our family in Aberdeen."

I agree with your decision that it is "Present Continuous used as a future form".