Chrome was the first app I saw that found the technical way around to force taskbar pinning. Microsoft, sadly, didn't patch that out.
I think they must have recently fixed this, in Win 10 Pro at least. I installed Win 10 Pro yesterday, then Chrome and it did not automatically pin itself. Actually, if I remember correctly it even had a message at one point during the install describing how to pin it.
It is fairly easy to disable this functionality. I have seen at least one app do this already.