The file endings of gerber files aren't fixed in any way, but I struggle a bit to make a sense of those you linked to. From looking at it it seems like the following:
.plc: Silkscreen layer, plc = "placement"?
.sol: bottom layer, sol = "solder"?
.cmp: top layer, cmp = "component"?
.stc: Solder Mask Top
.sts: Solder Mask Bottom
.drd: NC Drill
I'm not sure about .stc and .sts. It definitely looks like the soldermask layer, but I wouldnt name it ".stx", since I would read it like "stencil component/solder", which could be the paste mask.