I think Horowitz was only half listening and assuming the other producer was clearing things up for the audience. You can see he is pretty pissed when he actually tunes in and realises the dude is giving an accepance speech as if La La Land had still won.
I'm not calling Horowitz a piece of shit, I think you're confused. Horowitz is the gentleman and hero of the day here. The guy who kept going on and on knowing they didn't win was wasting everyone's time and being a douche.