So, it’s a melee weapon. It can be used as a ranged weapon, but it’s a melee weapon.
The contention was (as I understood it) that the rules say a weapon must be melee or ranged. The hoopak is both, but it specifically calls out the fact.
Personally, I don't really care for "a weapon that can be used to make a ranged attack isn't a ranged weapon", as it's a little counterintuitive, but I suppose it's the same reason a short sword deals piercing damage, despite having an edge- it's the primary way the weapon is used.
So sure, you could throw a dagger, but it's primary use is to stab someone. You could throw a sword as an improvised weapon or smack someone upside the head with the butt of a crossbow in the same way, but these aren't the primary ways these weapons are used.
Amusingly, I'd be perfectly on board with a Rogue using Sneak attack with pommel strikes and the like, but that's neither here nor there- the DM is allowed to bend the rules when appropriate!
Actually, thinking about it, this might be a good use for the Tavern Brawler feat, to allow Rogues to use their Sneak Attack with all sorts of weapons that they normally would not be able to, by using them in unusual ways in addition to using things that aren't intended to be weapons (Riddick and his damn tea cup for example). But that of course, would be a house rule, and I don't foresee any of my players going to such lengths when the game gives you plenty of perfectly cromulent weapons you can use as a Rogue.