Sure. It's possible, but as the article you linked noted:

   But American academic Professor Steven Kaplan, who published 
   a book in 2008 on the Pont-Saint-Esprit incident, insists 
   that neither ergot nor LSD could have been responsible.

   Ergot contamination would not, he says, have affected only 
   one sack of grain in one bakery, as was claimed here. The 
   outbreak would have been far more widespread.

   He rules out LSD on the grounds that the symptoms people 
   suffered, though similar, do not quite fit the drug.

While the "symptoms" listed is just a report from a single person nearly 60 years later are scary, as someone who took LSD dozens of times I have to agree with Professor Kaplan that the effects mentioned don't comport with my experience.

That doesn't mean it didn't happen (or that the CIA wouldn't have done such a thing -- they've done much worse), but the "evidence" is pretty thin IMHO.