In the Sawbill Outfitters blog, there's a picture of a brook trout that was caught on the lake. Entry is dated 6/3/17 but says the brooky was caught on May 30th.

Sawbill Blog

it does happen on rare occasions , where someone has caught a brookie in a lake that was never stocked whether its from a waterway connection from a stocked lake to an eagle having one in its talons and dropping it((i caught a walleye once in SAK that had puncture holes from an eagle that did have it for a moment)) , or with fish eggs/spawn cling to a feeding birds legs that gets deposited into another lake and i'm sure there,s other explanations too .

Sawbill Creek has trout in it. Most likely is that the fish swam upstream, I'm sure the water temp in the lake in May is pretty tolerable for troutskies. Wouldn't surprise me if there were more in the winter.

..or maybe they fibbed to throw you off and protect their honey hole. Do fisherman do that any more?? They should..