Wait.... this article makes no sense. So subscription revenues are going up, and subscription revenue as a percentage of total revenue is going up. That's great. But why is this an indication of success of the paywall? Seriously...
Paywall limits access to people who pay (subscribers) => more people pay => Times gets more revenue. What's not to understand?
Additionally, in print media, subscriber revenue surpassing advertiser revenue is huge and not something that would be likely to happen without a successful digital product for a couple reasons.
Beyond that, yes, there's nothing here but correlation. However I think there is enough in the first two paragraphs to make a case.