It seems that someone, who had originally claim on this title, sued the distributor. That's why it got changed in the last minute.
It also sets out to pastiche the "grindhouse" cinema phenomena, with the original idea of two films being shown as a double feature at drive-in movie theatres from state to state, with both films often being re-cut and re-edited, not by the filmmakers, but by the theatre owners themselves. This is evident in the amusing switch in title; with the film opening with the caption 'Quentin Tarantino's Thunderbolt', before awkwardly cutting to an obviously out of place title card with 'Death Proof' crudely emblazoned across the screen.
Even the title card, jarringly superimposed over the opening credits, looks like a last-minute replacement for an original title (“Thunderbolt”) that was changed by, say, a flighty distributor who got sued by someone who had a prior claim on that name.