Unfortunately, I think Zac may have inadvertently given away that a backup will be starting Game 1. He was asked about possibly signing an outside QB before the season. Here is the quote in question:
"At the same time, there are a lot of nuances to our offense where you're asking that guy to learn that quickly and be able to operate in a game, it's a challenge."
The concerning phrase here is "learn that quickly." If you're just bringing in a backup QB who you think is better than Browning or Siemian, and you think Burrow is going to be fully healthy for Game 1... why would you be so concerned about the backup QB learning the system quickly? In many years, the backup QB never really is needed. If it takes an extra week or two for the newly signed backup QB 100% up to speed, that would be fine... if you thought your starting QB was healthy for Game 1.
Sure, you want to have your bases covered just in case he needs to come into a game. But just the fact that this was the first thing on Zac's mind... how quickly he could get up to speed... it's just another sign. Is this quote absolute proof that they think a backup is starting Game 1? Absolutely not. But it may be a hint. I really hope I'm wrong on this.