That's a standard formulation, made famous by Virenque in 1998. Possibly even by Merckx in each of this three fails. Someone spiked my bottle. It was an honest mistake, guv, honest.
Or, basically, a big boy did it and ran away.
Edit : After double checking, he never said that phrase, it was the writers of the puppet show Les Guignols who attributed it to him and it became embedded with his character, mimicking some of his excuses and his style. Leaving my following message as is as an humbling experience.
I guess you're thinking of
"Dopé à l'insu de mon plein gré" which doesn't translate well because Virenque conflated and misused two idioms creating an oxymore.
"Doped unwittingly, of my own free will" is the best approximation I can make. Should have said "Doped unwittingly" or "Doped without my consent". But Virenque never was famous for being a sharp mind or Renaissance Man on a bike.
While you're right he was probably reaching for the "spiked bottle" excuse, the amusing formulation could be read as "there was a doping program I was subjected to without my knowledge".
He never lived down that phrase, I know he's still used as a prop whenever there's a sketch on doping (including for the 2023 ITT in the Tour) though he quickly gained back some public affection. He's seen as too naive or simple to have doped out of Machiavellian impulses (unlike Lance the supervillain) despite the investigation showing he was fairly proactive. Damning by faint praise, perhaps, but I suppose there's possibly a kernel of truth to that (all riders maybe don't have all their agency when facing that choice).