I would be extremely surprised to find out that was how it happened. More likely we (Mozilla) just have contacts at Telefonica from our Firefox OS work, and Telefonica happens to have this opentok software which provides a useful piece of making Firefox Hello work, so co-branding was a win/win.
Going with that line, was the inclusion of Hello such a complex thing that it needed to be bought in from outside of Mozilla - I'd assumed that using WebRTC as a video chat component made things [relatively] quite facile which is why there are so many implementations popping up.
What's the essential feature that Telefonica brings to the table that makes it worth Mozilla compromising their brand across 500 million installs [using Wikipedia figures there] - that's essentially saying that what Telefonica bought to the table is worth, what, > $5 million [assuming 10¢ per install for the brand placement]. Can you expand on the "win/win" part on the Mozilla, and their supporters, side?