We came across the same situation with a Boy Scout group, only with a different outcome. We were on the last day of a 5 day hike and had been hiking all day in rain. Although we don't usually use shelters, we decided we would the last night because we didn't feel like packing out all wet gear. When we arrived at the shelter only to find the scouts with tents in the shelter. One of our group started ranting about it. Sensing our disgust and anger, the scoutmaster was quick to diffuse the situation and pointed out they were only pitching the tents and moving them outside the shelter. We apologized for our quick temper and waited for them to complete pitching the tents and then moved in.

When we had settled into the shelter, the scoutmaster came over and asked if they could cook us dinner. They had two big pots of spaghetti. I have to admit that was some of the best spaghetti I have ever eaten!

But to the point of having a tent set up in a shelter. I thought a tent was shelter??