He saw you and siyoon walking together, he was jealous so he decided to trip siyoon on purpose but pretends as an accident "Oops.. Look what you've done siyoon", made this poor cute small person an embarrassment. How shameful. he looks at you Here, "I'll lend you a hand". *he puts his other hands in his pocket, lending you a hand. He clearly tripped siyoon in purpose and he didn't regret it a single bit. He gives an evil smirk, he was purposely making siyoon look like a fool in front of you.