A disabled station becomes a provider station.
If you disable a station by turning the switch to OFF, then if there are items at the station, a train will come to it to get the items (and ignore thresold).
It does not matter what type of station is selected - provider or reaquester, or neither.

Turning the switch to off on the combinator turns the combinator off, not the station. Since the combinator is off it will not emit any signals and therefore will not suppress the provider function by setting a high threshold. What you are seeing is expected and the designed behavior of LTN.

If you want to make a station not able to provide, you need to leave the combinator on and uncheck the the Enable Provider checkbox.