Fingerlings, by appearance, are often tweeners. FWIW, every physical marker I know of points towards this one being wild. Perfect translucent fins, very pronounced eye spot, red adipose, red spots as opposed to orange, non-distended anus, etc.
That's not to say a fingerling couldn't screw me up, and as troutbert says, location is an important consideration.
1. If a source of wild browns is obvious and a source of fingerling stocked browns is not, I'd call it a wild brown without blinking.
2. If wild browns are rather rare and fingerlings relatively common in this location, I'd still say it's likely to be one of the wild ones, but I'd be far from sure of myself.
3. If both are common in this location, I'd be a strong lean towards wild, but not 100% sure.
I'm thinking the body shape is probably what has you questioning. It's a rather fat fish with a small head; football shaped. While that's common on stockers, the CAUSE is growth rate. This is a youngish fish that grew fairly fast. But that occurs in wild fish as well, if the stream and their specific holding spot offers enough food to do so.