I had a similar experience in my first half marathon. It was the first running of this race and the only reason I ran it was because I got a free entry. They were still working out the organizational aspects and one thing they didn’t get down was that they had the 5k walk and half marathon race finishing at the same time. I came across a wide line of walkers literally stretched all the way across the road. When I called out, a few looked back and saw me coming but not one of them gave me an inch. I ended up having to push my way through them. Someone tried to make a deal at the finish line of my forceful way of getting through but a race official quickly stepped in and said they should have given me room to pass if they didn’t want me to push my way through.
Actually, to me, this may be as big of an issue as wearing headphones itself. Race officials should have a plan to handle finish line traffic if they have something like this going on. One race I do (Madison Jingle Bell) keeps 5k runners on one side of the road and 10k runners on the other side as the courses rejoin each other near the finish. This is just one example of how simple traffic control measures can at least minimize the risk of issues like this in the first place.