Unique situation - did I make a huge mistake?

[BCVI]

Hello, everyone. This is my first post; I hope I'm in the appropriate forum.

Last night I was playing at my friend's regular home game and I found myself in a unique situation.

We were about half way through a NLHE single rebuy/addon tournament (past the rebuy/addon period). There were 7 players remaining (top 3 got paid). The blinds were 100/200 and the relevant chip stacks were:

BB ~ 1700
Player A (under the gun) ~ 6700
Me (2 to the left of Player A) ~ 7800

Player A raised to 600. The next person folded. I called with KJ. The next 3 people folded. The BB reraised allin. Player A called the BB, and then incredibly forgot that I was still alive in the hand and turned over his AQ. Even though I was behind I figured I had the odds to make a correct call (especially since there was a chance that both the BB and Player A had an ace), so I called.

The flop came K74 (rainbow, I think, but Player A didn't have a flush draw, for sure). Player A checked. Now, I know that in this situation, the normal strategy is to check down the hand and try to eliminate the short stack. But in this unusual situation where I knew that my opponent completely missed the flop and I made top pair, I decided to bet allin.

To my amazement, Player A called. I turned over my cards and the BB also turned over AQ. One of the two remaining aces came on the turn, so I lost most of my chips in the side pot and Player A and the BB split the main pot.

In retrospect, the only ways I could have won any money with my allin bet after the flop is if:

A) I went all, Player A called (which obviously is not very likely to happen, but incredibly it did in this situation), and my top pair held up,

or

B) I forced Player A out with my allin bet and the BB held a hand such as QQ that would have lost to me in the end (but we would have both lost if Player A had still been in the hand).

So, what do you think? Did make a mistake by betting after the flop? Should I have checked it down even though I knew I had Player A in a huge hole after the flop?

Thanks in advance for your responses.