The short answer is "don't long press on the icon, just touch it".
This is the "App shortcuts" feature. If you just touch the icon it will open the app, but if you press and hold it offers shortcuts to whatever actions the app developer thinks people are most likely to want. The feature itself has been around for about 5 years, but more apps are using it now. Google do not provide any way of disabling it. You could try giving feedback to the WhatsApp developers, telling them what you don't like about it, and seeing whether anything happens. That's an extreme long shot, but probably has marginally more chance of getting a response than complaining to Google.