I never really thought about it, but yes, a fine without an admission of guilt is precisely a bribe. Consider the trade: you pay X dollars and in return they bury whatever evidence they have against you and you don't go to jail. Doesn't that describe a bribe to a cop or a judge or a prosecutor? As a corrallary I find it interesting that the media reports fines not as a fraction of net worth, but rather as an absolute amount. Clearly this serves the interest of both briber (who wants to be seen as punished more than it is) and the bribee (who wants the revenue, no matter how little it harms the briber).
