> There is no such thing as ownership of bitcoin.

That’s like arguing that there is no such thing as ownership of land. (Which some have argued, but it is a bit tenuous.)

If I post my private key to a bitcoin on pastebin and 100 people download it, who owns that bitcoin the moment before someone does a sweep transaction when 101 strangers all have the private key?

If I throw some money in the air towards a group of people, who owns it before one of them catches it?

I would guess that I still own it. In the same way, you still own the bitcoin until someone else does.

When you throw money and it's floating in the air and not in your hand, you can't spend it.

When I leak a private key and the coins remain unspent, I can still spend them.

Tossing money into the air clearly ends my ownership of it. Pastebinning bitcoin keys does not (at least until someone sweeps the coins somewhere else using that published key).