A Bloat of Hippopotamuses

I couldn't find this term in dictionary.com, or in any of the physical dictionaries in our house (and we've got a few).

I did find lots of websites that give "a bloat" as a collective name for a group of hippopotamuses. In some cases it wasn't the only one.

This example from the BBC website claims to reveal quite why a group of hipppos is called a bloat; but in fact, as far as I can see, it does so only obliquely. It describes the term as "witty and whimsical", and I think we're meant to picture a group of hippos in a way that fits the description.

One site I found gave eight different collective nouns for hippopotamuses: a bloat, a crash, a dale, a herd, a huddle, a pod, a raft, and a thunder. So to describe "a bloat" as "the collective noun for hippopotamuses" (my italics) is stretching it somewhat.

(Last week, in the Cup, a clash was a group of rhinos – along with a stubbornness. And a pod, according to the Chambers Dictionary (13th edition, 2014), is "a school, esp. of whales or seals; sometimes applied to other animals, fish and birds.")

As far as I know, hippopotamuses are the only creatures that have ever been said to gather in bloats. What a good job this question wasn't asked the other way round!