Also, adding to this. Tommy Tallerico has, in the past, clearly shown that he is not above selling off his sounds as royalty free sounds.
as evidenced by: https://www.sound-ideas.com/Product/200/SFX-Kit-Sound-Effects-Library-produced-by-Tommy-Tallarico
This SFX kit contains over 19,000 sounds that amounts to 6 gigabytes worth of death sounds, water sounds, walking sounds, explosions, laser sounds, helicopter whips, electrical zaps, motorcycle vrooms, among many others. It costed 700$ during first launch and now costs half that much. It could be likely that the oof sound specifically could have been one of those 19,000 separated among 7 CD roms. Even if not, it demonstrates that tommy clearly has the ability to sell off his sound to make them royalty free.
Roblox, probably had the CD rom at some point, though it’s been 15+ years since buying it so expecting roblox to still have it is a ludicrous expectation.
It’s possible that he could have sold the sound to a number of different sound vendors and not have remembered doing so. So roblox could be in the right here.
Plus, we never got a statement from tommy for what he was asking roblox for, he could be asking for thousands of dollars for a one second sound. Something that deserves maybe 20 dollars at most.
Still, it is entirely possible that he sold the sound off a very long time ago. And while, yes he does own the rights to the sound, if he sold it for someone to use royalty free, the disk holders can use that sound, royalty free. The likelihood of this being what happened is very high, and I’ll have to side with roblox on this one, because copyright law should not be abused.