Totally, there are more factors that play into it than simply spraying your leaves + light = burns. You'd have to spray your leaves and they would have to remain quite stationary, and close to your lights, for over five minutes (I did mention inadequate airflow in there). But, I know it is a possible occurrence outside as I have seen the leaves of my veggie plants affected by it, primarily cucumbers and of course they were in direct sunlight while they were hosed.
I just wouldn't go so far as to say it is 'total bullshit' or some kind of 'myth' or 'old wives tale'; it just isn't. Preventable? Sure. Old wives tale? Not so. Even during sun-showers, or when the sun comes out shortly thereafter it having rained, it would still be at least somewhat cloudy and the sunlight filtered; as the freshly fallen rain continues to collect on the leaves of plants, run-off and evaporate as the leaves shutter. To say that any plants would have gone extinct due to it is more than a stretch. It would be rare in the natural world (before humans with garden hoses/spray bottles existed) for the aforementioned reasons, but even if it did happen it wouldn't mean certain death for the affected leaves and so certainly the plant would survive.
I have never witnessed clear blue skies within ten minutes after there has been any notable amount of rainfall. I have absentmindedly sprayed down veggies in direct sunlight and after-wards witnessed necrotic spotting on leaves, and I've seen indications of it on pictures posted on this forum. However, I wouldn't claim the former scenario an impossibility and you shouldn't construe the latter an absolute absurdity.