Literally that was his first professional race that was truly tactical. He might have been gunning for top 8 and thought that the best way to do that was to track it. Certainly not his best result, but he did well to even make the final.
Something I found interesting, and encouraging: his last 800 was run in 1:53.5 (last 400 in 54.5) and ran 3:46. Exactly two years ago, in the Junior Boy's 1500, he ran a 1:54 last 800 and ran 3:58 (last 400 in 53). So he's certainly improving. He was just overmatched by, in order:
The best kicker in the US and perhaps the world
The best tactical 1500 meter runner in the world
a 3:53 miler with 5 years of NCAA experience who ran his best race ever
The best American collegian 1500 runner who was 4th at Olympic Trials
a 3:36 runner who nearly beat Cheserek and ran a great race
a 3:34 flat guy 10 years his senior
One of the fastest NCAA 1500/milers, but a beatable guy theoretically (Prakel)
One of the fastest NCAA 1500/milers, but a beatable guy theoretically (Thompson)
The D2 NCAA Champion, perhaps a beatable guy theoretically (Ribich)
The most talented NCAA runner in recent years, even if he's been hot and cold, perhaps a beatable guy theoretically (Saarel)
That's a very strong lineup. Hunter BEAT (an admittedly injured) Murphy and (a self-sabotaged) Blankenship. Those are two guys one wouldn't expect him to beat. Maybe he could have beaten Saarel, Ribich, Prakel, and Thompson, but there's no reason to expect he'd beat any of them. Three of them are faster than Hunter on paper, and Ribich has years of NCAA experience. Hunter did well not to finish DFL. Knock the learning experience spin all you want, but this really was a learning experience, and he will be a lot smarter for it. It sucks that he has to learn this in the USA final rather than the PAC-12 meet, but that's the way the chips fell for him. Lucky for Hunter, he's 19, and has a very long while to figure out how to place highly. Things will be easier for him once he's running 3:34 or 3:32, not 3:38.