I tried hanging a bathrobe hook from my sheetrock (not the joist) and one little tug ripped the rock. I would not do that again.
But you were pulling across the opening, That's called "sheer force" on that I agree put it in the joist. In the ceiling the sheet rock is thicker, and you would be pulling down straight. As long as an anchoring system was used, toggle's or those things that spread out acrss the BACK of the sheetrock it should be fine. If "mollies" (anchors that just stick in the hole and spread against the hole wall) was used the no it will not hold.
I install alarm systems and after 15 years I can tell you sheet rock is stronger that most of us give credit for. I have slid between joists in a ceiling laying on the sheetrock and it never moved. on the other hand I have stood up and fell through.
It's a matter of weight distrubution