It absolutely does matter if it's a currency, since as you state...

5) “Property” means any article, substance or thing of value, including, but not limited to, money, tangible and intangible personal property, real property, choses-in-action, evidence of debt or of contract. [1971 c.743 §121]

While BTC is "intangible," it still must have "value" to be considered property.  There is absolutely no way to establish that BTC has any value whatsoever, though.  That's the thing about a digital but legally-unrecognized currency.  Humans didn't make it.  There is no human value tied to it yet.  You'd have a better chance arguing that it has value to computers since it is the product of a computer's work and is recognized as work by other computers.  It isn't like traditional property (whether tangible or intangible) that is tied to the product of a human and therefore can be given a value in relation to humans.

Computers made BTC.  Although the program was the product of a human, BTCs are not.  They are a product of computers and computers alone, for no human can make BTC.  Because of this, it's even hard to establish that BTC constitutes property.  

The only exception to this is if the BTC were purchased with USD or some other form of property.  If they are purely mined, then I'm not sure they are anyone's property.  So, actually, I'd like to revise what I originally said...

If the sender can prove that these exact BTC were purchased by him using USD or some other property, then I think that legally he has a claim (although then there's still the question of whether or not he 'mistakenly sent them' as I described in my other post).  However, if he cannot prove this, or if in fact these BTC were mined and arrived purely on his exchange through deposits, then they are not even his property to begin with and he has no right to reclaim them.