If it is a 4x4 ,Any of the transfer cases I have seen on these late model trucks usually have their own seal and the output housing of the transmission has its own seal and there is a passage for leaks to get away , I wouldn't think it's possible to leak into the transfer case. The transfer cases are very small in capacity also usually 1.25-1.5 quarts.
If it continues to leak fluid , you may consider adding UV dye to the fluid to help locate the leak.