They should have cleaned the res tank out if they switch coolant brands on you.
The brown coolant and sludge is what orange dexcool coolant used to be. Over time it breaks down and when it reacts with air it turns into that nasty brown crap you see. So they just likely did a check coolant exchange and shipped it. The other part that sucks is that all that brown stuff is still going to float around for a long time in the coolant and mix with the green coolant and make it all nasty again. It takes many flushes to get all the brown stuff out.
