Is this Puzzle a bug, or..?

I didn't know how to screenshot, so I will post the PGN. It was a pending puzzle.

[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "?"]
[Black "?"]
[Result "0-1"]
[SetUp "1"]
[FEN "8/8/8/8/8/3r1k2/1K6/8 w - - 88 129"]
[Puzzle_Length "6"]
[Tactic_line "Ke2 Kc1 Rd2 Kb1 Kd1 Ka1 Kc2 Ka2 Rd3 Ka1 Ra3#"]

129. Kc2 Ke2 130. Kc1 Rd2 131. Kb1 Kd1 132. Ka1 Kc2 133. Ka2 Rd3 134. Ka1 Ra3#
0-1

Anything is winning, so what is the point of the puzzle? (I played Ke3 for the first move.)

what

50 move rule is a draw if you do anything else: so you need to find the fastest mate

It is move 43 of the 50 move rule: you need a mate in 6, and according to the engine: Ke2 is just that. Ke3 is a mate in 8 

How do you know if it is a 50 move rule?

what if it was the first move, you could assume that right?

It's in the FEN, bit if you're ever presented with a mate no matter what type tactic, it's always going to be finding the fastest mate.