This all relates to licensing, which is either subscription (Office 365) or perpetual (volume license and those cards sold in retail stores). If you're anything else, such as VL/Retail, or Subscription and <10.13.2, you'll be offered 16.15.1 with the '2016' moniker.
If you're activated with an O365 Subscription (as per the about box), and on 10.13.2 or later, you will be offered the 16.16 update and no '2016' moniker. However, life is going to get interesting on 8/14.
For the July update (which will be 16.15) it'll be business as usual and you'll still see the '2016' moniker for updates. Here's the skinny on how things are going to play out this year. It may help you understand what to expect. I'm reposting a message that relayed to us on Slack. This is a change from the way Microsoft has named and versioned its products. Version '16.x' and the '2016' or '2019' product names are unrelated.
