Yes, and also the presence of a window fan on that side is a big deal because the selection is based on scent. In my experience dogs appear to "like" a scent based on how strong it is, not necessarily how it is "flavored" (for examples, dogs can behave as if they love the smell of poop or skunk spray, but it's actually the powerful sensory information that they're reacting to, not a culinary desire). It seems possible to me that the dog is choosing whichever scent is more powerful.

Yep, I have seen dogs that clearly have "a side" for certain habits, even if it is not obvious whether it is paw preference, training, comfort...

Author here, yes, that's correct.

The initial set-up was to do 3 comparisons of the 5 treats (30 trials), alternate between right and left hand, then write a quick python script to randomize the order.

A bit more than halfway through the experiment, I ran the model and realized that A/D/E were the only contenders left, so I removed the B/C trials and added more A/D/E trials.