How did an ADVENT MEC target my soldiers with micro-missiles without knowledge of their location?

Question

I had two soldiers fully obscured from the MEC; they had no line of sight to the MEC and the MEC hadn't previously seen them. On it's first turn, the MEC fired a volley of micro missiles which hit two of my soldiers. As far as I can see, there are three possible explanations:

• MECs can sense units without line-of-sight
• MECs will sometimes 'grenade-spam' enemy positions, hoping for lucky hit
• The AI is cheating

Which of these is the case?

Answer 1

The MEC missiles are fired without the need of line of sight, similar to how grenades work. It needs to be aware of your soldiers but it doesn't require line of sight. Aware meaning that any foe has spotted any of your soldiers (you get the short cinematic where the enemy NPCs yell and point at you etc).