If, like CA something like this is an Infraction and not a Crime, then merely being stopped and arrested/detained for it in the first place is enough to make the subsequent search fruit of the poison tree...
True, but in the "broken-window" crime suppression theory, ignoring infractions breeds crime. In this "broken-tailight" Supreme Court issue, the operator was at least unaware of the failure of the vehicle to meet state code, despite the counterclaim by the ACLU "defenders." And perhaps the officer was sensitized by some other indicator(s) not chargeable but enough to raise a flag. And in fact, his inquiry
did uncover criminal behavior.
Such test cases are always chosen to probe just how far the envelope of propriety can be pushed by those wishing to implement greater lawlessness and less accountability for one's choices.