Here are illustrations of seven extinct mammals. The first is a raoellid, a group which might be the sister group to whales. The next six are more and more derived whales. All of these critters have been known about for a few years; none of them are discoveries made this year, with Maiacetus being the most recently described four years ago.

If we had to make a hypothesis on what the first whale's ancestor looked like, it would most likely look a little like extinct mammal #1 and extinct mammal #2. Four relatively thin but not very long legs, long-ish tail, head somewhat like a fox or wolf's head. So that's what this article should say. What does that article say instead?

All whales and dolphins are descended from terrestrial mammals, ancient creatures that were very similar to the modern hippopotamus.
Raoellids and the earliest whales are not similar to the modern hippopotamids.

Biologists aren't entirely sure which creature modern cetaceans (dolphins, whales, and porpoises) are descended from.
...we have a 99% confidence that modern cetaceans are descended from earlier cetaceans, and we have a 99% confidence that cetaceans, in general, are descended from other early artiodactyls.

The traditional theory suggests mesonychids, an extinct order of carnivorous ungulates (hoofed animals) which resembled wolves.
This traditional theory was rejected about twelve years ago; there are people reading this article who were born after this theory was rejected. So why bring it up?

But more recent genetic analysis points to artiodactyls, a hippo-like creature.
Analyses, because there's been more than one genetic analysis. Artiodactyla is a wide diverse group of animals that have been around for at least 55 million years, more likely 60 or so. During that time they have had, and continue to have, a lot of diversity.

There's some of the modern diversity. None of that modern diversity is what whales evolved from 60-55 million years ago, and to state that artiodactyls are "whale-like creatures" is akin to saying primates are tarsier-like creatures.