I certainly wouldn't count it out but I'd be inclined to check everything on the cold side first. The odds are probably higher that a line didn't get sanitized or a spot on a tank was missed than spontaneous inoculation. Im just assuming here but I feel like if that was the cause then you'd probably have run into this issue before.That's a good idea with the growlers. It was windy that day and took a while to chill with the immersion chiller. I'm thinking we may have picked up something while it was chilling uncovered. Another reason to break down and buy the plate chiller.
So in doing some digging I found my German APA idea isn't so original lol. I guess Victory did it a few years back with the same hop though their approach to the grain bill was more American than mine. While somewhat discouraging its not uncharted territory its also a good sign I'm probably in for a great beer.
"Below is a description of CBC Mandarina Pale Ale from the Victory website:
'CBC Mandarina Pale Ale
Pale Ale
A blend of German pils and caramel malts combine with German Mandarina and dry-hopped Mandarina to create a full bodied, citrus-hopped brew with a pleasant bitter finish and lots of hop flavor.
Composition
ABV: 6.0%
Availability
Special one-time release, March 2013”