I agree there's not much of a difference, but I'm not sure if Galen could run that fast right now.
In 2016 he was competitive enough to get 5th in the Olympic 10k and come back for a medal in the marathon. He was at least attempting to do both types of training. His lack of speed in the last 400 of the 10k showed (but then again the same happened every year except for 2012).
In 2017 he got 5th at USA's although he was coming off of Boston which was much later in the year. With not having done a marathon in a while maybe he's good to go, but at this point in the year, you're in heavy marathon training. Plus, he's years removed from doing any sort of 10k racing or possibly 10k specific work.
Unless he's attempting the 10k/marathon double again I think it's just a test run to get the legs going. Like we've seen with M Huddle, each marathon you do and marathon specific build-up you do, it makes it even harder to go back to speed work (and obviously you get older). We even kind of saw this was Flanagan when she kept coming back to make 10k teams (her last attempt was 2017 and she was 4th).