Well from the information that screenshot gives us we know that they are the only two players ingame with mics connected and both of them are muted.
We know that they are the only players with microphones connected purely because every cod game's voip works the same, it displays a little speaker symbol if the mic is plugged in, if it has bars next to it they are talking (the bars represent sound) and if it is crossed with a red x they are muted. If instead of a small speaker we see a small, low detail drawing of people if they are in party chat.
Here are a few possible causes we can draw from that:
- You have previously muted them
- Your playstation network settings deny you from using voice chat with players not in your friendslist
- Your settings automatically mute voicechat if you don't have a headset in
All of these are things you will need to check yourself in both the settings of the game, and of your playstation 3 console.
Also there is the possibility of it being a random glitch, evidence of other players encountering this is found here: https://www.gamefaqs.com/boards/995751-call-of-duty-modern-warfare-3/61848344
It is not a ban, a glitch. Has happened to me before, and some random person i was playing with. If you want to talk with someone party chat works, it will probably work the next day
So it is possible that this is just a temporary issue.