Boosting the ISO will increase noise, but it won't have any effect on focus. Of course, low light means a wider aperture and a shallow depth of field, but as long as the subject is right at the focal distance, that won't matter much either. There is definitely visible noise, but you nailed the focus.
I was on the pier at sunrise (probably about 5:30 AM) and the light was LOW, so I had to boost the ISO a lot.
Ironically, the bird was almost too close because the minimum distance of my telephoto lens was about 4 meters.