I think Laura detects the scent before her father starts gunning the engine to drown out MIKE. By the end of the scene she isn't certain if what she's just experienced is something truly sinister or a case of road rage. Leland covers his tracks by admitting he was home. You can see Laura just desperately hoping that what she's suspecting isn't true.
Fire Walk With Me does warp the series, but there are still those visual or aural cues that we recognize. Hints of the series' soundtrack will briefly appear. Visually, there's the mystery of the recipient of the second half of the necklace, the safety deposit key placed in the diary, the interior of Harold Smith's home, the stoplight, the flashlight beams in the night, Laura hysterically handling the dirt that will later form the shrine in the train car in the drug deal sequence, the appearance of the pale horse, the Fleshworld adverts, Julee Cruise's singing revealing the interior thoughts of one or more people in the Roadhouse, Laura's prom queen photo in the school and her livingroom, the whirring ceiling fan, the dark at the top of the stairs, music in the air, Waldo the bird as the sole witness to the crime--- all recognizable landmarks from the series that seem even darker here.
Got up early, found something's missing/ My only name/ No one else sees but I got stuck/ And soon forever came