I think that's disingenuous. Running is his immediate, panicked, fight-or-flight reaction to Sage's revelation, and his mind is in turmoil over it throughout.

To give the lines I quoted a little context, here are the paragraphs immediately preceding:

Then a thought blindsided me. An idea worse than Sage's confession. Worse than the knowledge I'd made out with a boy.

I'd believed Sage was a girl. But does everyone else?

Now that I knew, Sage's true sex was fairly obvious. Did anyone else guess? What if Jack or Tim figures it out? What if they thought I already knew?

On my hands and knees, I vomited all over the rubberized surface of the track.

I don't think many readers will conclude that his throwing up has nothing to do with Sage.