That website seems... not great?
I think you got a 50x ratio by dividing the average prices of $0.12 (Italy) and $5.94 (Canada).
That appears to be a median...but I'd like to know how they chose the plans they used for the calculation. For example, Canada's maximum price is given as $46.02/GB. Perhaps such a plan is technically available, but I really doubt someone is using it for data, so it seems bizarre to include it in this data set.
For cheapest prices, they cite $0.05/GB for Italy and $1.66/GB for Canada. But off the top of my head, Rogers, which is the #1 telco in Canada, offers $0.74/GB. Seems... odd that it didn't make it into this dataset.
(And hey, I would like to know where I can pay $0.05 to get a GB/data in Italy. Full speed? On a good network?)
I pay $29/mo for unlimited data in Canada. Granted - with caveats! It gets throttled after the first 6 GB. I wonder if this would be counted as $4.83/GB in this survey? Their methodology PDF is unclear.