You can see their whole menu here [2].
Obviously, McDonald's thinks "Supermac" and "Mighty Mac" infringe/dilute its own "Big Mac" trademark.
I don't know why this article seems to be presenting this as a fight over chicken sandwiches. From their menu, Supermac is clearly a burger chain that also has chicken sandwiches, just like McD's.
I'm genuinely confused as to how McDonald's could have lost this. McDonald's sells Big Mac sandwiches (using the Big Mac name) all over Europe. So none of this makes any sense to me.