Jack clearly doesn’t die from a fire. There’s quiet a few clues.
They want us to think that Kate started a fire that Jack died in – but if this show has made anything clear, it’s that what you think is wrong.
So, we know Kate thinks she’s responsible for his death, but she’s also an unreliable narrator.
They are setting us up, as they have before, until they pull the rug out from under us.
Reasons Jack didn’t die in a fire:
After we see the kids crying (which doesn’t necessarily mean the scene we are seeing after is directly after that, time wise), we see Rebecca wearing the same shirt she wore 17+ years ago when they watched the Super Bowl at the bar she sang at.
You don’t happen to be wearing during a fire.
Also – she’s riding with Jack’s stuff in the passenger seat.
How did that stuff survive? It would burn in a fire. There’s a reason she has them, and they weren’t in a fire.
Obviously Jack has died before this fire.
For all we know, they don’t even still live in this house; just because we see the children grieving doesn’t mean the cut to Rebecca is right after that. At the time we see Rebecca at the end of this episode, she is clearly still grieving his loss by wearing that shirt and keeping his things in the passenger seat.