I watched the Today Show interview and saw video of him prior to that where we could see from his running form that his leg muscles were in trouble. I don't know whether out to was looking for attention when he crawled but I was glad he tried to downplay it in the interview and also he commented on not finishing within his time goal.
Regarding the need to finish without aid I thought I would mention I blew up with heat exhaustion during my first 10K road race on a hot summer day. It was the summer before my freshmen year and I was there with my XC coach and some teammates. I knew little about road racing did not take much water on the course. It turned out one of my relatives who was in the race ran up behind me after I fell and helped me. I don't know if I was in sight of the finish line. I was out of it mentally at the time and for some time afterwards but I recall thinking and probably telling my relative that I needed to finish by myself. I was thinking of the Olympic marathon racer who was DQ'ed for being helped to the finish line. See link to video below. I did not finish that day and was taken to a hospital because I was not recovering fast enough there at the race. I did not start to come out of the mental haze until the air conditioning of the ambulance cooled my body. So I am saying that if one is in bad enough shape they are not thinking clearing enough and may attempt to crawl to the finish without aid. I don't know if this was the case for this Boston runner. My 2018 Boston Marathon was on pace for the first 8 miles or so before hamstring issues occurred in both legs. I had problems with one leg for months before the race. When the 2nd one tightened I changed my goal from BQ time to just finishing the race without walking. I briefly thought about quitting but then thought I was at Boston and I was not about to quit or walk the course no matter how bad it would get. I want to finish and earn the medal. I would want the volunteers at the finish line to give me the opportunity to get across the line unaided. I thought those that ran marathons were a little crazy. Now that I have run marathons I think we need to be a little crazy because we are at a high risk of blowing up in many ways. It puts an incredible stress on our muscles and organs. We aren't doing it for our health. We are doing it to prove to ourselves that we can accomplish something mentally and physically challenging.
Regarding collapsing at or near the finish of a marathon I thought I would try to sprint the last roughly 200m at one race. I started sprinting and within a few seconds my head felt like it was floating. I immediately slowed my pace down as realized that I may faint if I continued that pace. So some runners are likely picking up the pace to an unsustainable level when the finish line is near. Once I cross the finish line when I switch to walking I often have trouble walking. My legs will buckle and even after that I cannot walk a straight line--I need to take an occasional side step to catch my balance. I needed the help of volunteers at the finish of the 2017 Chicago Marathon to walk after the finish and at the 2018 Boston Marathon finish I almost hit the ground when my legs buckled. An observant volunteer at the finish caught me and handed me off to someone else who handed me off again to someone else who then put me in a wheel chair. I sat in the aid tent for about 10 minutes before I felt that I could walk unaided. I might have to resort to crawling across a finish line if I slowed to a walk before the finish line. One of my goals is to never allow myself to walk any portion of a marathon. Part of the reason is to take the easy option off the board to give up and part of the reason is that walking may be more difficult than continuing to run.
https://www.youtube.com/watch?v=r6xU6DiRKCg
So those like me that are collapsing at the finish line are likely suffering from the following:
https://us.humankinetics.com/blogs/excerpt/making-sense-of-why-runners-collapse