A few clues
1/ would not sign a new 100,000 a week contract
2/ went to Chelsea for a medical
3/ says he wanted to go to Spurs
and 4/ Most importantly has shown no sign since Koeman went that he feels any different
I am quite happy he is on his bike!
1-3 happened on Koeman's watch. Maybe it was a coincidence and he was just done.
However, let's face it from Day 1 pretty much he was Koeman's whipping boy and the one that was dropped and/or chewed out in the media. Koeman tried to get in Sigurdsson in pretty much every transfer window before this one so maybe he knew he was for the chop as soon as his replacement came in and started making plans.
Regarding 4, he's not said anything before or after in public so nothing has really changed there. Personally I don't mind that, I'd rather he dealt with the club directly than via Twitter.