What causes scrambled egg patties to turn greyish green on the inside?
Yes, too high temp will/can turn egg yolk blue-is/greenish/grayish.
But doing it in microwave will probably not. Mostly beacuse it's harder to heat anything inside than outside in a microwave.
From experience I can tell that in places made to feed a lot of people in short amount of time any breakfast items are premade and then just keep warm. So the patty would be cooked in temperature allowing inside to be done an then kept in an oven or over the lamp. Making inside of the patty to still boil (as energy exchange is slowed) allowing sulfur o bond with water in patty. The longer the heat is provided the longer this process take place.
A) the patties are safe too eat but they might be rich in sulfur
B) you might bought the food some time (few hours) after it was made and it wasn't made fresh
Overall nothing bad but personally that is something I would expect from a food stall rather than restaurant.