Glad it went well!
The actual "decoction" is the process of taking a portion from the mash and heating up to boiling. When you boil it you "burst" some of the enzymes (as I've seen it referred to,) which adds a malty flavor that you can't get from specialty grains.
When you add the boiled mash back to the main mash you are only using the heat to bring your entire mash temp up to the desired level. In this case you overshot the mark, but the actual decoction sounds like it went just fine.
I would ask how long you were above 170f as that can cause some astringent flavors by releasing tanins from the grain husks. As long as it was not above 170f for too long ( a few minutes should be OK) you will not have a problem.
Did you REALLY overshoot, or did you not stir enough? Just curious. I have had my wife monitor my Temp Guage on my B3-1000 and she goes "154... wait it JUMPED to 170... OK back to 156..." while I'm stirring
I find if I stir it long enough (at least 5 min) I can get a better reading.
Let me know how it truns out!