Getting Messages even though it has been disabled for years

I just received a text in iMessage on my mac. This is quite surprising, as I haven't owned an iPhone since 2014, and I subsequently disabled iMessage on all the macs I have owned since. As can also be seen in the screenshot. "Aktiver Meldinger i iCloud" is Norwegian and means "Activate Messages in iCloud". So, given that background, how is it that I suddenly receive messages that would otherwise be sent as SMS?