Did you use dry yeast? If so, maybe when you pitched, some of it got caught or stuck somewhere above the level of the wort. And for some reason when you racked to a secondary, it came loose and got in with the beer being transferred.
I also wouldn't use a secondary just because the recipe said too. I tend to think much of the secondary recommendations come from back in the revival of home brewing in the 80's and earlier when people were trying to rationalize the use of bright tanks by the commercial brewers. The main reason they used them is to get the beer out of the FV that they need to start the next batch. FV's are more complicated and expensive than bright tanks are for the commercial beer. That's why they don't just build another fermenter.
On the homebrew level, you can just leave everything in the primary FV and the same things will happen that happen in both your secondary FV and in the commercial brewers bright tank.
If you need your FV for another batch, another FV is a reasonable expense if you are doing that much volume of beer making.... on the homebrew level.