This title is misleading. The term "release" suggests U.S. soldiers were/are being held prisoner. There are not.
The title of the article you cited is: "U.S.-TRAINED NIGER JUNTA KICKS OUT U.S. TROOPS, DRONE BASE." Nowhere does the article say that American troops/personnel are being held prisoner in Niger.
The junta would not allow any flights to resupply the troops with food or medical supplies nor would they allow them to leave. They were in effect held hostage, though not in name. The junta wanted something from Biden in exchange for letting them leave, and apparently they got whatever it was they wanted..................