You mean like it being mentioned by Fabrizio Romano as being bullshit?
Sancho is not going to come out say that straight away that would be dumb for him, he would only break his relation with Dortmund and that wouldnt warranty him moving here so not much to gain but a lot to lose.
What makes more sense for you.
A) its a, lame, tactic they anounced after the deadline to put more pressure on United on buying him asap by saying he wont be cheaper next year because they secretly extended their contract.
B) they did secretly extended their contract just by one year, without anybody knowing. In times when is basically public knowledge of every god damn player in the planet how long their contract is.
Additionally this would have happend at least one year ago because they been trying to renew Sancho for one year now and has refused.
Come on mate, it doesnt takes much to realize this is a clear bullshit tactic.