I noticed, but I believe it is simply a result of its left eye being exposed to sunlight first. This happens to me a lot, because I instinctively close one eye when it's sunny. I do hope I don't have dain bramage.
It shouldn't matter which eye is exposed to day light. Both pupils will adjust to a bright light even if one of them is still in the dark. Alexander is right that in humans this is typically a sign of head trauma and brain damage.
You can actually do a little test of this in the mirror. Get close to the mirror and focus on one pupil. Then either close or cover your other hand with your eye. Your uncovered pupil will also dilate. Then when you uncover your other eye the uncovered pupil will contract again.
There is a complicated explanation involving light-sensing ganglia in the retina and data being processes in the visual cortex, but it is too long and I would probably get it mostly wrong anyway.
And just incase people comment that the pupil is reacting to a lack of light rather than an increase of light the same thing happens when you introduce a light source.
Looking into the mirror put a barrier between your eyes (this could just be your hand) With your free hand aim a light at one of your eyes keeping the other in shadow. You will see the pupil constrict in both eyes equally and simultaneously.
Thats alright. I'm a 3rd year nursing student so i know exactly what you mean.