Yeah that was just an example of what ISO can affect on your image. Your sailboats you said were shot at ISO 100. I'd bet 400 would have brightened the image nicely and might have even sharpened the shot a touch. Back in the old days, action shots were all shot with ISO 800 or 800 "speed" film. The lower the ISO, the longer the shutter has to be to adequately light the sensor.Good example!
I can most likely change iso in a photo editing program?
The Nikon system camera I was using at that time was max iso 1600 and with boost 3200 if I'm not mistaken. But with iso 3200 the image quality was not good, not even on the small screen on the camera🙂
The newer ones goes probably higher I think🙂
Apps like Moment or ProCam allow you to adjust ISO manually and your Nikon should allow you to provided it's not a basic PnS. My Pentax K70 has a shortcut button on the main dial that opens up the ISO dialogue.