AI always generate different outputs for the same input (AI appears to be non-deterministic) so it would be impossible to confirm that exactly.
But I suppose what they mean is they appear to be of the same quality. Taking a longer time does not appear to decrease the quality of the output.
I suppose you could give an AI the same input resetting it after each input and then use statistical models to identify common traits. Then do the same thing on different hardware and run the same statistical analysis and see if there is a difference between group A in group B but as far as I’m aware no one has done this.
In theory hardware shouldn’t matter, it’s all mathematics basically and one plus one is always equal two, so there shouldn’t be any fluctuations.