Not really it is pretty standard. As for all the other questions around contract neither party would want that in the public domain. In fact there would would be a confidentiality agreement as part of the settlement agreement.
Some arrangement will have been agreed and he may have a moved lined up once recovered from injury. So becoming free agent means deadline day no longer applies to him.
So probably suits both parties.
Exactly this, had a move scuppered by injury but by leaving and becoming a free agent he is not restricted by deadline day.
He obviously wants regular football, good luck to him.