From that gif, I think Eunsoo cannot be blamed for being inattentive or careless. From the direction they were going, Mariah was the one who could notice Eunsoo first, she came from behind and whisked by Eunsoo. Mariah had the right of way, but Eunsoo already stayed out of way by skating slowly close to the board. Maybe Eunsoo could have kept her eyes on Mariah all the time and stayed really really far away, I don't know. I can not say for Mariah's intention or non-intention and whether the bullying were the truth or not, but Eunsoo was in no way at fault for the situation happened on ice at that moment.