Why do you find it so hard to believe? Only because you never saw a box that said "Ferrania "?
The Kodak - Fuji monopoly/duopoly case was widely debated throughout late 80s and 90s (just one
example). Never ever did Ferrania (nor Ferrania/3M) enter the debate. You can guess why.
You are, of course, encouraged to come up with any half credible link to support that Ferrania was at anytime anywhere near to being largest C-41 manufacturer in the world. Sorry, but that claim has all the "Pentax 17 camera accounting for 20% of entire Ricoh's revenue" vibe. "Ferrania being world's largest C-41 manufacturer" statement probably started as something like "Ferrania was largest
white-label colour film manufacturer in
Europe" and then morphed into this. Frankly, it's quite absurd that this is taken seriously on Photrio.