Googling around shows the claim has been much-repeated, but without much if any additional detail to lend credence. Given Tesla's long history of outrageous claims, I wouldn't believe it until I saw some evidence.
Transferring power that far would require quite a large transmitter and receiver You'd expect a picture or something would exist.
If I may go off on a bit of a rant, I find the cult of Tesla somewhat annoying. While he did make some important contributions, his fans tend to dramatically exaggerate them (often taking his own claims at face value). I guess part of the reason is that simply makes a good story (if you ignore many facts) he was indeed a bit of a crackpot, which fits nicely into the 'mad scientist' narrative. You have the whole "War of Currents" narrative, AC vs DC, Westinghouse vs GE, Tesla vs Edison. You have the poor unrecognized Tesla versus the rich and famous Edison, etc. I don't think anyone's ever been as famous for supposedly not being famous as Tesla is!
The reality doesn't make for quite as exciting a story. Tesla was fairly well-known, even in his lifetime. He had a rich backer (Westinghouse). There's a US-centric aspect in that the "War of the Currents" was largely an American affair, at a time when the USA was not yet the center of the science/engineering world. Tesla didn't invent AC. Many of his inventions had already been invented or patented in Europe, or were independently invented around the same time. The world's first long-distance AC transmission system was built in Germany (1891), by AEG, without Tesla. Westinghouse built the first commercial AC system in the USA at Niagara, Adams in 1895, but it seems often forgotten that they did buy technology from Siemens. Also overlooked is the fact that a commercial AC system was taken into use in Sweden* in 1893 (before Adams) by Wenström/ASEA (now ABB), using his designs. Most notably it was a 3-phase system, unlike Tesla's 2-phase. (and it's 3-phase we use today for generation/distribution). People will probably be debating until the end of time who-did-what-first. But in any case, Tesla was by no means alone.
Tesla was big on claims, but when you look to the ones he ended up delivering on, they're mostly things that were also independently developed by others in roughly the same time period. Now either you can hold the view that Tesla was the greatest inventor ever, and that Marconi, Dolivo-Dobrovolsky, Wenström, Steinmetz, Edison et al were ripping him off. Or you can conclude that the inventions he's best known for were not quite the singular achievements they're often made out to be.
(*Fun fact: In an odd twist of fate from the "War of the Currents" perspective, Wenström's original AC transmission line is still used by his company - for testing HVDC transmissions!)
