What an amazing family business they have.
Update: Fangoria: FX Artists François Dagenais And Tenille Shockey On Fiona Dourif's Mind-Blowing Transformation
One night, Fiona decided to take her Charles Lee Ray makeup for a "test drive" and went out to a bar while still under full prosthetics.[...] "Fiona decided to hit on the waitress as 'Charles' to try it out."
The soft focus was a give away that it wasn't de-aging, since digital F/X crews haven't quite cracked that one yet. (There's a debate about whether Lynch used de-aging for the Laura Palmer flashbacks in Twin Peaks: The Return, all the more murky given the intentionally dodgy CGI used throughout the series.)
Nevertheless, it took me a while to realise it was supposed to be a young Brad Dourif and not a young Tommy Wiseau because of the glasses.