Warzone Assault Team Selection

Does anybody know how the teams are selected on Warzone assault?

I have had 15 games now and I have been the attackers twice. The team selection obviously isn’t random. Random would imply a 50% chance of being on either team. The probability of running a scenario with two equally weighted outcomes 15 times and having one outcome occur 13 of those times is roughly 1/312 (0.00320435). Somehow I don’t think that I have been that lucky!