To be quick, it seems that the Master of Shadows always references the player as being in the Order of Whispers regardless of actual order affiliation.
By being in rhe pact they kinda were. Plus, despite reputation traveling around the world, it may not be totally accurate
I'd rather keep going.. wherever the wind takes us
It's not just a reputation thing. The Master of Shadows says his information came directly from the Order of Whispers.
R.I.P., Old Man of Auld Red Wharf. Gone but never forgotten.