That IS odd. I wonder what on earth they were thinking. Maybe if the public footpath went through their pasture and they were constantly getting people and dogs walking through, perhaps they began feeling unsafe about it? That is really strange. Ive had them run up to eat, and run up to play before, but never just all decide to attack. Huh.
Just goes to remind us, all animals are unpredictable. Always be watchful, even with trusted pets. You never know when they are in pain or scared and might do something dangerous like bite, or in this case, go on a trampling spree. ;)
Glad you're okay!