Quick rock paper scissors question

[Dale Dough]

I'm in the WTF how is this even an angle shoot camp.

If it's 'because he can see what you do and quickly curl up his fingers to make scissors', can't he do the same thing if his hand is horizontal? Throw rock and then quickly extend two fingers?

I mean, I don't see how this is any more of an angle shoot than pretty much any effort to change your throw at the last moment.