It was apparently described that way in an old Lucious Bebee photo caption, and unfortunatey, the stupid name stuck.
No C&S man would have the slightest idea what you were talking about if you referred to their cinder catcher as a bear trap, he'd think you were plum loco. Might as well call it a Dagwood Sandwich.
I gave up trying to discourage use of that silly name years ago. It's become railfan lingo, like the word "loco", which to me still means crazy.
The reproduction cinder catcher made by Tim's Dad, who is in the picture, was made of aluminum, and was thought to be able to withstand the rigors of heat on a working engine. That it apparently didn't is news to me, but I haven't been in the "loop" on anything to do with that stuff for a long time. The original C&S cinder catchers were made of sheet iron, and are extremely heavy.
Ridgway, who was head of the C&S Mechanical Department in 1918, was directed to develop a cinder catcher to eliminate threats from the US Forest Service about heavy fines that were to be assessed on the C&S for fires started on the Clear Creek Branch at that time. This design was far more effective that the silly little cone shaped beartraps (why not call the little cones beartraps too?) that were used before.
By the way, that skinny character leaning back on 74's sand dome in that picture is me, about 50 pounds ago. Well, maybe 40.