"...the opening seemed strange and I wasn't sure what to do..."
If he leaves something that he should have taken, then you take it yourself. Simple logic.
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At move 7, he is unusually low. Why fight him for the low side?

Position at move 7
- Click Here To Show Diagram Code
[go]$$ Position at move 7
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$$ | . . . O . . . . . , . . . . . O . . . |
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$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . W . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . X . . . . . X . . . . . X C . . |
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I can't say that this is better, but feels better to me. He neglects the center, so you seize it.
If he tries the same two space extension on the right side, the power of your Q16 stone can be felt all along the side.

- Click Here To Show Diagram Code
[go]$$Bc
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$$ | . . . O . . . . . , . . . . . O . . . |
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$$ | . . . . . . . . . . . . . . . . 2 . . |
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$$ | . . . , . . . . . , . . . . . , 1 . . |
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$$ | . . . . . . . . . . . . . . . . X . . |
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$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . X . . . . . X . . . . . X C . . |
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$$ ---------------------------------------[/go]
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At move 13, the hane at N4 is good because it is the place that he wants to play next.
But by that logic, we could go back one move and look at what he should have wanted to play then.
Back on move 11, P2 was the textbook move for black. It makes black safe and solid. Taking it yourself hurts black even more than N4.

- Click Here To Show Diagram Code
[go]$$Bc
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$$ | . . . O . . . . . , . . . . . O . . . |
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , X . . |
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$$ | . . . . . . . . . . . . . . . . X . . |
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$$ | . . . . . . . . . . . . . . O O . . . |
$$ | . . . , . . . . . , . . . C X , O . . |
$$ | . . . X . . . . . X . . . . . X O . . |
$$ | . . . . . . . . . . . . . . W . X . . |
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$$ ---------------------------------------[/go]