The source is TBR and FourFourTwo have just recycled it.
https://tbrfootball.com/heung-min-sons-camp-shocked-after-what-tottenham-have-told-them-about-new-contract-in-u-turn/
The headline is a highly misleading because the article for TBR goes on to say, "Sources have told TBR the north London side are ready to trigger the extra year in Son’s current deal which is set to expire in the summer." The FourFourTwo article says, "The north Londoners have the option to trigger another year on Son's deal – and will still likely trigger that to keep him until 2026."