the two are related.
1st clue- something big happens to Hank, Janet and Hope in the mid-credit scene, traditionally a teaser for an upcoming film. Turning them into dust...
2nd clue- next/upcoming Marvel film is IW.
3rd clue- Antman is going to appear in IW next as Paul Rudd has been filming for IW. His next appearance is not Ant-man 3, but IW. Surely events of mid-credit scene are going to be related to IW and not Ant-man 3.
4th clue- half way through IW we learn Thanos' end game is to erase half the universe.
I'm sure Hank, Janet and Hope disappearing in the mid-credits has nothing to do with this even though the villain just said he's going to kill off half the universe
...it's not even with the benefit of hindsight. Once you're watching IW, it would just be obvious the two events are related.