Curious Companion on Cavalier

I've been using Curious Companion for quite some time on Cavalier, and thus far, all of my DM's that I play with when I want to run it have had no problem. Mixing this with Saurian Champion is a fine way to simulate having a Juggernaut Beetle (Don't forget to slap the draconic archetype on there to add on its acid resistance and acid spray!) while playing a Duergar, for instance.

But another player just pointed out to me that by RAW it shouldn't work.

Indeed, I misread and thought it said that you must have an animal companion. Not that you must have the animal companion class feature.

Does having an animal companion (granted through mount) count as having that class feature? The few instances I can find of others discussing this, that seems to be how they interpret it, but I wanted more opinions. Does this work by RAW?

Does it work with RAI? Had Paizo ever intended for this sort of combo to work?

In the end, I get that we can home brew whatever, but it got me curious!

Compare curious companion to the beast rider feat. Probably your use isn't RAI or RAW, though as you say you can homebrew it.

That is a perfectly valid GM ruling, since the Mount feature of Cavalier "functions as" the Animal Companion feature of a Druid. Go forth, strange rider of bugs!

Strict RAW, you need a class feature called "animal companion" to select the feat. Of course, that means that neither Druids or Rangers can select it, because they gain their animal companion from the Nature Bond and Hunter's Bond class features, respectively.

I don't think anyone believes that's intended or how it should be handled.* We probably all agree that everyone able to select any animal companion can select that feat. The question thus lies whether someone with a very restricted selection can take it.
My take is that Cavaliers can take the feat, but the "The creature must be one that he is capable of riding and is suitable as a mount." part of the Mount class feature rules is still intact. The Cavalier can only select a creature that fits between their legs, roughly speaking.

*) The feat is from Wilderness Origins, a softcover book, which are known to see precious little editing, plus it was written at a time where the focus of the development team had already shifted onto PF2. Not that such errors don't appear in the CRB and other books - the Command Undead feat asks for "Channel negative energy class feature", something that doesn't exist in the CRB (as the Cleric class feature is just called Channel Energy, no matter the type you channel).

Wow, druids too, huh? That does make it seem kind of weird.

What class actually gets just "Animal Companion" then, as opposed to receiving an animal companion from something else?

I know it's a long shot, but is there any way to get an author to actually comment on the feat then to clarify? Disallowing druids seems unintentional to me.

Wow, druids too, huh? That does make it seem kind of weird.

What class actually gets just "Animal Companion" then, as opposed to receiving an animal companion from something else?

An actual class feature named Animal Companion? Hunter, Wild Child Brawler, Sacred Huntsmaster Inquisitor, Sylvan bloodline Wildblooded Sorcerer.

Honestly though, there's a bunch of examples where class features aren't properly called. Wizard's familiar being a prime example, which comes from the Arcane Bond class feature, and thus RAW doesn't qualify for e.g. Evolved Familiar.
And of course, there's plenty of other situations where using the strict RAW is ridiculous. A Wild Shape using Druid literally turns into an animal because the polymorph rules only apply to spells, a style feat's stance never ends, Shield Master required an FAQ to not remove Power Attack and other penalties (and Simple Weapon Proficiency still does that), proficiency feats don't grant proficiency (and a Witch gets light armor proficiency as a bonus feat), Form of the Dragon grants 11 natural attacks... I don't think anyone follows these rules to the letter, and feats asking for "animal companion class feature" belong in the same group.