Well AFAIK, there's something to it. Dr. F somewhat addressed this once,
here.
Basically, enough heat + oxygen will give you metal oxides, which with their nanoparticle size and frail structure, could potentially be an unwanted byproduct in the aerosols we inhale through our vaping devices. The structures of metals change drastically at certain temperature ranges, so this would be especially true with dry burning. It is also possible that if you don't dry-fire your coils up to welding temperatures, they may never oxidize enough to toss off anything more hazardous than the air people in philly breath every day. This may even be the case either way, since I'm willing to bet that nobody vapes at anywhere near 700+ degrees. At this point, there is a lot of testing still needing to be done when it comes to the specific applications of the materials being used in the context of "vaping."
Is it a possibility worth considering? Hell yes, it absolutely is. Has enough research been done? Absolutely not. It's not a question of whether or not small amounts of metal are being inhaled at this point, though this itself is a point of contention, as there is not enough data to substantiate this as a fact. We're just going off of what we know about how kanthal reacts to specific temperatures in a general sense. That data is not always so relevant when it comes to specific applications. Normally, fairly rigorous testing is done, even on products that are made up of things that are proven to be safe, before they hit the market.
With vaping, this has not been so because it was basically a home-brewed innovation and the market still has no regulatory oversight because the government is still too busy trying to figure out if we're smoking or not, so the research has not been mandated. It's a wild-west of information that will hopefully get boiled down as legitimacy becomes more established. For now, I would take any claims swinging to either extreme with a boulder of salt.
It is at the very least assumed that metal oxides are being generated, if not inhaled. The question right now is, what is the amount that ultimately hits the lungs under typical vaping conditions and is it harmful? That's what we want to know right now.
Thus far, there seems to be no reason to assume that they are. It sounds scary when someone says that you're breathing in metal, but the fact of the matter is that it's in ALL of the air we breathe, just like formaldehyde. As with many things regarding health and safety, it's all a matter of degrees.
Unless this guy is a scientist with access to journals that lay-folk don't or is on the bleeding edge of vaping research, he's full of shit. It's either that, or he holds the answers to questions the entire vaping world is still pondering. Either way, what a dick!