This is something quirky that sometimes happens with female grouse!! Sometimes they get really enamored with a human for some reason, which is pretty funny. Check out these videos:
http://www.youtube.com/results?search_query=friendly+grouse&nfpr=0
Sometimes they are attracted to vehicles like ATVs, because of the low frequency 'putting' of the engine is similar to a male grouse drumming... but who knows why they are so friendly with people?! I think it's really cool.