Um yeah it was for real. And I still have a lot of those older hens, although many have begun to pass away. There's a story behind it that I will save for another day.
The hens that carried MG were a group of 12 ISA Brown pullets that I purchased from a local seller at point of lay. One died before I sent the second off for a necropsy at my state lab. Several others were very symptomatic for months, while the rest never showed any symptoms. After I learned why they were sick and then read everything I could find about MG, I built another coop and run, separated by an expanse of woods, for chicks I bought at tractor supply the following year. I took precautions including wearing separate shoes when tending to each flock, and the new chicks/adults were never exposed to the carrier flock. The original ISA Browns all passed away from natural reproductive causes before their 4th year. I will never buy chicks from anywhere but a reputable national hatchery due to that first experience. And I know I was lucky they only had MG. There are many tragic stories on this forum where people were so excited to get chickens, then discovered their flock was sick with multiple incurable diseases. I'm sorry it happened to you.