I think that there's some science involved that affects why some folks experience flash rusting while others don't.
This page lists a lot science about it based on empirical evidence and references about flash rust. --->>>
https://www.canada.ca/en/conservati...conservation/understanding-flash-rusting.html
Whether it actually applies or not, for some reason this paragraph seems relevant because it mentions that water can be absorbed by the top layer of metal which along with the RH of the water and salts and particles present can be a cause.
When the metal begins to heat up there must be some kind of steam effect that creates some higher humidity close to the surface of the metal.
"Corrosion at high relative humidity
The term “flash rusting” usually refers to corrosion of wet iron and can begin within minutes. Iron exposed to high relative humidity (RH) also corrodes, but more slowly. At high RH, even if the iron does not appear to be wet, the surface is covered by adsorbed water. The thickness of the water on a metal increases with RH, becoming several molecules thick at high RH(Leygraf and Graedel 2000). The corrosion rate increases rapidly above a certain RH, called the critical RH, which is about 65% RH for iron (Phipps and Rice 1979). Above this RH, there is enough adsorbed water on the surface to resemble bulk water and promote corrosion.
Rusting of iron may also be promoted if impurities such as dirt particles, salts (such as from fingerprints) and acidic pollutants are present on the surface (Rimmer et al. 2013a). These impurities can attract and trap moisture next to the metal surface, thereby promoting local corrosion. Regular cleaning to reduce deposited dust from metal surfaces will help to reduce corrosion and damage to the surface (Thickett and Costa 2014).
Many salts are hygroscopic (take up water), and so can produce moisture on the surface of iron, even at relatively low RH. Dust accumulating on the surface of bare iron is often the source of these salts. These may lead to local corrosion spots when these salts pick up moisture."