One of the perks of being a naturally awakened S-Class is your body turns into steel when in danger!
The fangs of a few B-Grade monsters have nothing on you!
It may sting a bit, but they won't be able to tear your flesh!>
That was what the System told Wonhee while she was being bitten by those monster wolves, hence she was able to remain calm when those monster wolves tried to eat her.
If Wonhee, a newly awakened Guide, had that much protection, then she expected that the members of the Big 4 would have a sturdier body than she did. Hence, she was surprised at how EASILY Yejun broke Graham's arm.
Not only that.
Yejun also stabbed Graham's hand with his ice dagger.
[I don't know if the System lied to me, or did it happen easily because Yejun is stronger than Graham?]