It's kind of hard to tell how the play unfolded from a few frames, but the MC went flying perpendicular to the side-line. Yes shoulder to shoulder contact is legal, but within reason. You cannot be "reckless" or use "excessive force." Whether a tackle is one of those is up to the referee. In this example, the MC got body checked and assuming he didn't dive, went flying. Remember he also scored two goals and was noticeably their key player. And so naturally, he would attract this kind of attention. So in my eyes, that challenge would be deserving of a caution. But again, it's hard to tell from a few frames and shoulder to shoulder contact is ambiguous.
P.S. Also ty for the chapter, I love this series.