I am very strict about people going into my chicken yard. Each property has its own bio/pathogen footprint. Your chickens build their immunity against the pathogens found on your property because they were exposed to it at an early age. You may have dangerous pathogens in the soil of their coop and home but they are not affected because they have built up immunity.
However, if you go to another chicken keepers house and walk in their chicken quarters, you are bringing in pathogens from your property and picking up new pathogens on your shoes. If you wear those shoes into your chickens living quarters they can become sick, not because the dirt from your friends chicken yard is bad but because you have brought new pathogens into their living quarters.
For this reason, if I have guests who want to see my chickens I will have them put on a pair of shoes that I have reserved for guests to ware in my chicken yard. I also keep those surgical booties to have guests put over their shoes before they enter my chickens living space to protect my girls. Most guests don't mind because they don't want to get chicken poop all over their shoes anyway. They underestimate just how sticky and nasty chicken poop can be.
Now during peak bird flu season (fall and spring migration) I will allow NO one into my chicken yard accept my family who wear only their chicken coop cloths and shoes to avoid bring the flu into my girls living quarters.
When I visit
Tractor Supply or any other feed store I will completely change my cloths and put on my chicken coop shoes before going out to see my girls. It is very easy to underestimate the possibility that you can bring illness to your flock by not taking processions.
In the Chicken world we call this Bio Security. It is doing your best to limit your flock from the exposure of other bio contaminants the could make them sick. It is something to take very seriously.
So yes, the breeder you visited was doing the right thing. He was practicing biosecurity to protect his flock from illness and disease. I would be very careful of having your friends kids play in your girls quarters if they have chickens as well. The exchange of pathogens can be quite costly if your girls get sick, and visa versa for your friend.
It may seem like over kill, but when bird flu has been reported near your area it is time to take some serious step to keep your girls safe. If it is bad enough I will go into what I call "Lockdown". This is where I will keep all my girls in the coop and pen. No one is allowed in the chicken yard accept for my family, no exceptions.