Floodwater is horrible. Full of sewage overflow, agricultural runoff, etc. Any building contaminated with floodwater will at the least need to have all the furniture, floor covering, drywall etc ripped out and replaced. Even then you’re rolling the dice that the timber in the frame won’t just grow mould forever.
Also does he risk his insurance rejecting the claim saying he caused the damage? Also although probably negligible your then making the flooding worse for your neighbors.
I assume not every building can do this, or else the city would run out of water? Or it depends where you live?
And at the end of the day, is it just a matter of aesthetics, that your walls don't get stained? Or is it doing other things to preserve value?
Won't the timber become moldy just the same?
And this is a restaurant. They already removed the furniture, there's presumably no floor covering, etc.