they can be owned by multiple people at once while maintaining different values for each owner.

Each NFT that you see is unique in its own way. Sometimes 2 NFTs might look alike but on the blockchain each one of them has its own unique owner.

An NFT is owned by a single user at a time. But the creator of an NFT always gets something when his creation is sold by another even after he or she doesn’t own it anymore.

Following Smith's work came CryptoKitties; a collectible game where players buy and raise virtual cats

If not for this post I would have never know that smith was the first ever to create an nft. The cryptokitties gaiend so much popularity that at one point in time I thought it was the first ever nft.

They are unique and cannot be duplicated

Yes, this is because each nft is unique. No matter the number. And as soon as it is created , it is stored permanently on the blockchain and each time ownership is transferred the blockchain records it.

Sure, it is very possible for an NFT to be stolen if a hacker gets access to the digital wallet where the NFT is stored

Unfortunately NFTs seem to be more vulnerable to attacks than cryptocurrency. In a space of about a week you can hear of multiple cases. But the good thing about this is that immediately it is stolen, it’s sale can be frozen.