I'm all for people having fun and trying things. We should not get too serious about all this. But you have to realize it is a fun thing to do. A one-off time is not a statistically relevent experiment. No matter what the results of this one sample, it will not prove the theory works any more than me getting all pullets in a straight run order from Cackle proves that all straight run orders from Cackle will give you all or mostly pullets.
In most scientific experiments, you hold the theory you are testing as the only variable. You run a test to set the standard, then play with that one variable to see if it gives consistent or consistently different results. I think this is pretty much the opposite. To prove this theory, not only would you need to hold this variable constrant, you would have to try it with all other variables all over the board.
If we can agree that the hen determines the chromosome that determines sex when she lays the egg, we can eliminate a lot of variables that have to do with incubation. No, wait. That is not true. Maybe if the incubator runs a little warm, the pullets are the most likely to survive and hatch. Not that incubation temperature determines sex, but does it determine which sex survives to hatch? Or is it humidity that controls that? I'm not sure. I guess we have to include even more different variables. Not as simple to set up as I thought.
Diet has been mentioned as a possible variable, so different hatches from hens that have been on many different diets. It has been suggested that certain hens throw more girls than boys, so eggs from many different flocks are needed. It has to work on round and pointy eggs. Eggs laid in the heat of summmer versus the cold of winter. Eggs stored warmer than the recommended temperatures and eggs stored cooler. Eggs laid with various planetary alignments and different phases of the moon. Maybe eggs that are large for that breed versus eggs that are small for that breed. Still air versus forced air versus broody, maybe. Eggs laid in the morning versus eggs laid in the aftenoon. Age of hens might be a variable. I'll ignore whether the incubator was in a car or truck, but you can include whatever variables you see fit. In other words, this would have to prove pretty consistent in a wide range of conditions on a lot of different hatches.
I'm not convinced that you getting mostly roosters with this one hatch would totally disprove the theory either. You might have applied it wrong. I think you would still have to do several more hatches with different people applying the method, before it was conclusively disproved. And if you get a statistically significant number of hatches, even a 5% variation would show there is something to this.
Like I said, have fun with it and don't get too serious about it. Keeping chickens is supposed to relieve stress, not cause it.