None of the articles specifically say "he was diving" or "he was snorkelling". And the people he was taking pictures of are referred to as "tourists".
I just found an article from Thursday's paper that leads me to believe he was snorkeling/free diving.
In short, the story says the searches had been extended for an extra day beyond the 72 hour legal search, even though at that point there was little hope that he was alive.
A high-ranking official of the Cozumel Marine section is quoted explaining that usually, when a person drowns in the ocean and the temperatures are warm, it takes two or three days for the body to float back up to the surface unless it is stuck/entangled, but that since the weather has been cold, it might take longer.
The fact that they don't mention equipment and only use the term "buzo" (diver) in the titles of the articles and nowhere in the stories themselves makes me think that the disappeared was not scuba diving.
But it's just a guess based on my translation/interpretation of a newspaper article, so don't take my word for it.