That's definitely weird to say the least... I wonder if they're looking in the wrong area perhaps? Must've gotten a phone call or something if police cordoned off the school in Choctaw though.
I Can't imagine how the person could've heard it that far away. Perhaps there was a crash or something on the Interstate near the same time?
A crash on I-35 would make much more sense. A resident from Choctaw they interviewed said that a car sped off from in front of his house right after the explosion which neighbors said happened behind a school.