I happen to work in Home Automation.. This is likely wrong, and I agree its probably dodgy router
Customers with a moderate amount of tech logging are sometimes our biggest bane. In this case, there's no information of what the washing machine is connected to. And no packet dumps.. Yes its asus too, so don't trust their routers at all (they aren't known for making good routers).
And then, we also constantly have customers picking out every single thing on their router too who think their information is being stolen or whatever because a service its connecting to sounds technical.
Then we also have the ones who get their info from places like Toms hardware, such as with CCTV, which "confirms" china is watching their lawn grow or whatever. Never any actual packet dumps, traces or anything else though.
Honestly, when you see an article like this, the first thing you need to ask is for packet dumps and such.
In practice, just don't forward your devices online using port forwarding, and use a strong password, good devices, and you're fine.