My understanding is that tech divers usually dive in a team of three, with each member strictly tasked to part of the dive requirements. Each knows their duties & responsibilities. This incident does not appear to be a team dive. I have no idea how extensive their dive plan was.
I agree with TSandM about positioning but I've found an almost total absence of any real discussion of a definite plan in diving with buddies or groups of three or even four. Usually even the buddy check is paid lip service. Unless something is obvious it is missed.
Maybe it's just my area but even when diving with a group led by the instructor that trained me the plan was basically "Follow me." Note, the group, except myself, were newly certified divers. Pretty much the same on boat dives on Bonaire. Divemaster said "We'll descend and swim in that (pointing) direction. When someone reaches 1500psi we'll turn and head back." No assignment of buddies, no real plan, no idea of what to do if someone wandered off or forgot to check their air. Note, the divers were bounce diving, running into each other, and pushing other divers. Divemaster out front paying no real attention.
I think having a real plan is really important when diving in a pair or group. Communication before and during the dive can make a huge difference. My experience is that this is the single most neglected aspect of diving. It might not make a difference in a pair/group that has been diving together for a long time. Between less familiar divers it's essential.