I thank you for sharing the camera stats, as I learn from the settings good photographers use. Here I'm surprised that your 4 K ISO isn't so grainy (where it matters, the birds.) I would have guessed you had a higher shutter speed. I seldom use ISO's that high, so maybe I need to start experimenting with them more often in my BIF photos. Of course different cameras behave differently. Mine is a Sony A7R III. I used to use Canon (for years) but still avoided ISOs above 2000 as the results were more often than not too grainy for my taste. I know high ISO numbers are heartily discussed by photographers. With the new photo software like Topaz DeNoise it can sure help.
I also learn from reading people's settings!
I almost always shoot in Manual mode where I control aperture and shutter speed but find when shooting moving targets, especially birds, that shooting in auto ISO is quickest (It was a bright day but harsh light, I'm surprised the auto Iso went that high too). I use to put a cap on the auto ISO though and it wouldn't go above 12000 or something. I've taken off the cap recently because I was missing some good shots that a bit of grain didn't seem to mess up too much. And like you've said, there are some great editing programs that help with that. I have only used Lightroom but I hear wonderful things about Topaz and I'm sure I'll try it out some day. And the cameras are getting a lot better at processing those high ISO images with less grain, too.