No, I'm pretty sure it's literally fog, some kind of aerosoled mineral oil.
Here is an example: https://imgur.com/a/gdemKM3. Notice the hazy background. The still is from this video [1] at 00:22, coincidentally also a good video about cinematic realism.
Here [2] is a video about lighting that shows adding haze.
Some cinematographers certainly use blooming filters, too. I noticed that Spielberg had a period with tons of bloom, though I don't know if those were filters or just a certain kind of lens. Indiana Jones 4 had absolutely awful photography. Bridge of Spies is also a good example, lots of blooming, lots of hazy indoor rooms.
