It's not dumb.
It's called projection.
It's widely used to predict box office of any movie.
Usually the margin error is not that wide.

It's a bomb given that production budget is 250M and marketing budget for blockbuster is usually 100M.
Overall=350M production + marketing.
Rule of thumb for movie is that cinemas will take 50% of box office money.
Means this movie needs to make 1.5x its productiob+marketing budget to break even. It needs to make at least 500M to break even.
Anything below that is a bomb.
Given how frontloaded blockbuster movie is, it needs to make huge money during opening week.