The puzzle is not complete. The complete main line is 5. Kc2 Rd4! 6. c8=R! Ra4 7. Kb3! 1-0
Ouch.
5.Kc2 Rd4 6.c8=Q! Ra4 7.Qh8+ Ka2 Qb2#
Even I know that one.
After 6 c8=Q Rc4+ 7 Qxc4 stalemate.
Cool i missed it promote the pawn to Rook ..