[thierrydamiba]

I think it’s a play on “who’s line is it”

[dools]

But whose line is it anyway is spelled whose because it’s a possessive pronoun. Who’s means who is or who has.

Who’s up for some donuts?

Whose turn is it to go to the shops?

Who’s seen my car keys?

[Asraelite]

In this context it's a possessive determiner, not a possessive pronoun.

[serial_dev]

Its still whose, sorry to tell you, your misstaken

[ohthatsnotright]

Their mistaken what?