Board Thread:Episode Discussion/@comment-24993958-20171021151743/@comment-4010415-20171024041438

I'm saying that the rule isn't "This enemy had to push them to their limits or what-have-you", I'm saying that the rule seems to be "This fight influenced them in some way; this event caused them to grow as a person".

Weiss' fight against the Boarbatusk wasn't some crazy hard task that pushed her to her very limits. However, during that fight, Weiss snapped at Ruby due to her frustration with the Boarbatusk and her annoyance about Ruby being leader. Because Weiss snapped at her, Ruby confronted her in the hallway. Weiss stormed off away from Ruby and went to talk to Port, the one who had her fight the Boarbatusk in the first place, to talk to him about class. Port prompted her to talk about what was bothering her, and through their conversation, Weiss was convinced to stop being pissy about Ruby being her leader and start working to be a better teammate.

That personal growth gets traced back to Weiss getting frustrated during her fight with the Boarbatusk and snapping at Ruby. Therefore, apparently that counted enough for it to become a summon.