Honestly? That claim seems a bit(read A LOT) exaggerated. I haven't had whatsapp in a decade and none of my friends(scattered all over Europe) or family uses it. Viber used to be a big deal and to an extent still is in some areas of Europe. Personally I think I've talked almost everyone into migrating to Signal.
In the Netherlands Signal is getting traction. I talk to most people via Signal, about 85% of my messages are via Signal. Which includes my parents, and I didn't even put them on Signal.
