Is this true?

Sounds like an urban legend to me. Visible light has no effect on atmospheric conductivity AFAIK, because it falls in the class of 'non-ionizing radiation'. 40,000 volts may sound like a lot, but it will only arc a few inches - not 20 or more feet.

Always be suspicious of emails that begin with phrases like "100% true"

It appears that Keshavani Hospital exists on the internet (nestled within many of the repeated versions of this story), but nowhere else.

I will be so bold as to brand it an internet hoax.

This is one of those anecdotal stories that answering the question "Can this happen?" should be broken into at least two parts.

First, as presented is it at all possibly true, no matter how remotely possible, that the flash of a camera can cause a high voltage arc path to occur in air. Yes, it is conceivable that the momentary air ionization from the ultra-violet light from a xenon tube camera flash might provide that last little bit of trigger energy to cause a high voltage line to discharge through the camera. However, for this to happen there will have to be so many hidden, helping factors that I would expect the odds of this happening to be literally astronomical.

Second, something else might cause a photographer to be electrocuted that a witnessing layman might think that the camera's flash caused the discharge. This seems far more plausible to me. There may have been a thin wire dangling from the transmission line that the distracted photographer wandered into. The vaporization of this thin wire provided both the initial flash and an ionized gas path for further heavier current discharges. There might have also been a coincident lightening strike some where on the power line. These would still be extremely unlikely but still possible.

Sounds like blue sky lightning....

"Please avoid talking on mobile phones while driving." and cautions that might apply to use of a charger have nothing to do with the situation described in the story.

But petrol outlets and railway stations are places where stuff happens that you might want to photograph, especially in Mumbai. I guess I'm in a cynical mood... can't help wondering, who would benefit by scaring people, so they don't use their phones to take pictures at the train....

I have some thing to share.I have witnessed ,a flash of spark stretch between a ODC* (over dimensional consignment) and 66 kv live conductor.Fortunately it got earthed through a metallic rod hanging on trolley and touching ground,creating a big path hole on road.But in the process all 64 tyres of the trolley got heated and were required to cooled by throwing buckets of water on them,which got converted in to steam,immediately.

This happened near Murtizpur (Maharashtra) and during summer and hot afternoon.

I remember I could see flash (bluish) in broad day light.

* We were transporting cement machinery to L&T Awarpur site.

If he was within the danger zone , I believe 3.3m for 40KV, there is a good chance that 40Kv could arc across, not from the flash, but the camera being conductive and possibly he raised his hands.

Absolutely unfounded.

First off the 19 year old gentleman did not only move off to a distance he climb on top of a tank car. In doing so he may have close the distance the live wire needed to go to ground. The flash could have been just a coincidence. The arc could have set the flash off or at the moment of the arc he had his finger on the button. Muscle restriction do to the arc on the body setting it of.

There are plenty of stories out there about this incident. None of which I find credible. Most list it as a hoax. Either way there is no scientific data to support that light can conduct electricity.