Can someone explain/confirm this please.

[TonyBlair]

Just played a NLHE hand where I had JsTs and the board was 9h qh kc. I ended up all in against Kh 3h.
I checked the odds and was surprised that I was only a very slight favourite.
I was more surprised when I changed the opponent's K to an Ah. This tipped the balance in his favour.

I'm guessing this info is correct but I just wanted to check. I'm guessing it's the backdoor straight that makes the A better than the K in this instance but I'm surprised that this makes the flush draw a favourite against the made straight.