A devil's advocate announces the position is borrowed. A concern troll insists the position is sincerely their own. The deception is the entire distinction — the arguments can be word-for-word identical.
Side by side
Aspect
Concern trolling
Devil's advocacy
Position is owned
Falsely claimed
Openly borrowed
Announced
No
Yes
Good faith
No
Yes
Can be identical in wording
Yes
Yes
What each one means
Concern Trolling
Posing as a sympathetic insider in order to sap a group's momentum — expressing worry about its tactics while actually working to undermine it. It is aimed at individuals too — false concern for someone's health or choices, used to criticise them.