Looks like he might have been the priest? Looks like a side altar. It surely isn't the main altar at a Cathedral, no?
The steps and above are a sacred space. Hallowed ground to some of us. The equivalent of the Holy of Holies in the Old Testament. Nobody is allowed there apart from those who are supposed to be there during Mass and the sacristans who set up for Mass. As a sacristan, altar server and MC I've had to remind people, politely, that you can't just walk up near the altar.
-Tim-