A "grey" import is one that wasn't brought into your country through official Nikon channels. The product itself is the same, but there are usually warranty considerations with grey imports, hence the usual slightly lower price.
Most resellers will tell you. Often it is clear - they'll say it's a USA model, or they're an approved dealer, or it comes with a USA warranty. Usually, if a product doesn't come with a USA warranty, the reseller will offer their own warranty which may mean that they have in-house replacement/repair capability or they have a contract with a firm that does. If it is a reputable business, you will probably be ok with their warranty. Often it comes down to personal risk tolerance considering the price of the item and the reputation of the dealer.
When it doubt, call and ask. B&H and Adorama are exceptionally reliable. Amazon is reliable as well.
But checking the B&H site again, it isn't clear whether it's a USA model or not. It isn't marked with either USA or IMP (for imported) - B&Hs usual convention. Nonetheless, they say it comes with a 6yr warranty in the box which would indicate USA model
I was confusing the VC version with the non-VC so that would explain the price difference.