I get that people don't usually expect to play against WW top, and he has his low health gimmick, but do those things alone make him cheesy?
I would define a cheese pick as something that requires your opponent to not understand how your pick works for it to be effective. While that's definitely not uncommon for this pick, I don't think it's necessary. Secheppo has been picking him top for over half a decade in Challenger on what's often considered to be the best server. More and more WW top onetricks have been reaching high elo in their respect servers.
If even Korean pros are getting beaten by it ~50% of the time, is it still cheese?
The reason I'm making this post is kinda petty I'll admit-- a Renekton I played against called my pick cheese. I thought it seemed like the pot calling the kettle black, as Renek is a lane counter/bully that becomes one of the most useless champs once first towers fall. At least Warwick has fantastic damage reduction, aoe cc, decent dps and isn't just a slightly tanky stun-bot.
This is definitely the case for many people. WW is not that common of a pick, and people don't really know how to play against it, so you can get away with a lot of cheese in lower elo's playing WW. I think that's where much of the salt comes from.
The thing I'd say also is kind of unfair about WW is that you can take awful trades, but heal up off of a single wave. So WW players don't need to really play the lane the same way most champs do. Hence why they have the brain dead player stereotype (somewhat true lol). You can just mindlessly run in, do some damage, fear or run away if there's a blood scent, then heal up off the wave. It's something no other champ can do.
Ultimately, it's just a different playstyle that other's aren't used to. Certain champs that have specific playstyles people generally hate playing against, like Illaoi (though WW is much more interactive than her in). In general, I don't think he's cheese, since playing against WW is really just knowing his limits and not to be baited by low health. Something a lot of players don't know how to do since he's pretty uncommon. He's not like, say, fiddlesticks top who I think is really cheesy.