New iPhone came with latest iOS version.

It was almost certainly a used phone, perhaps a return or a demo. Enter the serial number here→Apple - Support - Check Your Service and Support Coverage and see when the warranty expires. If the phone is new it should be 365 days after you purchased it.

And being in a sealed box is meaningless; the machines to reseal a box are quite inexpensive.

The iPhone 11 was discontinued by Apple in September 2022, when the iPhone 14 was introduced. iOS 16 was also released at that time, with iOS 16.1.1 being released in November 2022. It is highly unlikely that Apple installed that version of iOS on the iPhone 11.

It is quite possible that it would be updated, particularly if you bought it from Apple itself

It is not unusual for a newer iPhone to be delivered with the latest software. But it seems a little strange that the iPhone 11, which was discontinued before iOS 16 was released, should come with iOS 16.1. However, there may be exceptions if it is purchased directly through Apple.

If the box was sealed, then it is probably OK.

You can always check your iPhone's coverage to see when it is first activated:

Check Your Service and Support Coverage - Apple Support

Was the box sealed when you got it?

You are welcome, and a good idea to contact Apple directly.

Okay. Try following the link I posted in my first answer. Then you can check when the iPhone was activated for the first time, and that way get an idea of whether it was new when you got it.