To be truthful about it, everybody is wrong here. "iOS" didn't come out in 2007. It was originally called, "iPhone OS". Later years it was changed to iOS to accommodate the iPod Touch and iPad. 
In terms of it being called "7", that is correct. Apple is not naming the OS after how many years it's been in existence, they are naming it after each version that year. So 2007 has to be counted because that's when the OS for the iPhone came out.
In terms of it being called "7", that is correct. Apple is not naming the OS after how many years it's been in existence, they are naming it after each version that year. So 2007 has to be counted because that's when the OS for the iPhone came out.