En attendant Aline - Why do we use Le Futur Antérieur ?

Question

In the activity "En attendant Aline (Le Futur Antérieur)"

It's two in the morning, she must have had an accident! Il est deux heures du matin, elle aura eu un accident !

As per my understanding, Futur Anterieur is used for "past" (anterior) events in the future. In this context, there is no future.. They are discussing the possibilities in the past. Could someone else explain. I went through the lessons on Futur Anterieur and did the quizzes. I was able to understand clearly. But this particular activity, I could not understand. Please help.

Accepted Answer

Futur Antérieur is used to make conjecture about the past. In English, we tend to use "must have" when we really mean "probably had". We sometimes even use "will have". If I see my brother asleep at the keyboard, we can say in English "Oof, he'll have had a busy day", which is exactly the same as what's going on in French here: I'm making a supposition about a completed past action, even though I'm grammatically using the Future perfect.
For more specific info, check #2 here:
https://www.lawlessfrench.com/grammar/future-perfect/

Answer

Merci bcp Mon. Maintenant je comprends.