No, NASA didn't take a picture of a UFO

It probably isn’t clear, but the little grey cylinder that kind of looks like an unlabeled tuna can is the HDEV, or High-Definition Earth Viewing system, installed aboard the ESA’s Columbus module. That tuna can is also highly reflective, and so if there’s either sunlight falling on the ISS or external lights from the ISS itself turned on, you’re going to see a couple of bright spots shining off of that module.

Even though it isn’t obvious that’s what you’re looking at in Scott Kelly’s photo, another similar photo really highlights with great certainty that this is a reflection off the HDEV, not a UFO.