With the cross-country system of 7 running, 5 score, coaches often make roster decisions under the train of thought that they have two "extra" runners, and take a gamble with one and use the other as a safety valve. It presumably came down to Owens, Pons, and Yamin for the last two spots. Just from what I know of his high school performances, Pons likely has more upside potential than the other two- he's the gamble. If Owens showed more consistency than Yamin over the course of the year, then he goes as the safety valve.
What's confusing to me is why the "gamble" spot didn't go to Stilin who won IC4As on Saturday instead of racing at nationals.