Differences in how they did theirs, pretty much I think - different things grew more, others less, than what you were doing with your own. I've actually done this myself with the same grains - usually when I didn't refresh that often during times when I wasn't using that much kefir.
Unlike you, however, I don't really like that strong yeastiness - I got rid of it by rinsing the grains between refreshes for a while (normally I don't bother to rinse, seems silly) - then they went back to what passes for normal for me.