The context of the quote was that Goucher and a few other CO guys had a tendency to put on weight pretty easily. (Gouch, Sev, Batliner). If they lifted and ate college diets they would probably be a little big by elite standards. Wetmore was emphasizing being lean. After all, Gouch had to beat Lagat to win Nationals.
Now, it is a little ironical that Salazar is talking about muscle when Hasay seems to be excessively skinny. With her current build, she will probably not outkick anyone. Cain or Alexa would probably beat her at any distance to 5k. And with a couple years, they would beat her at 10k. Those two particular young runners are extremely strong.
Hasay's future is the marathon. She is built for it from head to toe.