This area simply provides viewing of the lions directly through glass at ground level, while a viewing platform on top of the cave gives viewing down onto the lions (and directly across if they are on the rocks). I suspect that it was just cave-themed as it was a dark area anyway, there is no signage about any links between lions and caves or anything. There is a daily keeper talk on lions, and it may be done in the cave area on wet days, but it is too small an area to accommodate a decent crowd, and on a normal day it would need to be presented on the platform above. I believe that this enclosure, including cave, was built in 1991.
I'm not sure when this was modified (I don't usually go in there) but I noticed on my most recent visit that all the stalactites have been removed so the ceiling is more even. Perhaps there were issues with tall people