I have no idea how they are counting it but I think there might be a grain of truth to this. iPhone users don’t choose iMessage specifically, it’s the default when texting other iPhone users. But how many people in Europe use SMS these days? It’s all WhatsApp, Messenger etc.
Last time I sent an SMS was like 7 years ago or something like that.
Companies still use them to send you verification codes (which depending on your country can be a mayor security risk) and reminders, but otherwise it’s mainly WhatsApp or other messagers like Telegram or Signal.