This is mostly a nothing burger. AIS has basically zero validation built in. I'm not sure where the article is sourcing its data from, but it's probably an open source ship tracking site.

AIS datagrams aren't encrypted, so you can make one with any ship ID and location data you want, then create a station account on one of the open trackers and inject it.

Alternatively, you could get a cheap SDR dongle and broadcast your spoofed messages to a nearby station and let them upload it. It's been a while since played around with SDR, but you could probably get everything you need for around $200. You'd almost certainly be breaking licensing laws doing this, for what that's worth.

Edited to add: Looks like this article is using kpler.com, where you can sign up to be a receiver station and feed them data.