The alpha he met while on the photo set of the Hyung he worked for. He asked him to pretend to be his boyfriend. He was going to spend his heat with him, but Asel backed out at the last minute. He was actually a really nice and decent guy.
So why did he sounded so hard on the phone?
He probably was 1) still butthurt about the incident with Asel and his heat and 2) Asel was running away from him for a reason so he was being protective. Remember Asel asked him to pretend to be his boyfriend, and he promised he would play that role.
Who is KANG WOOSEOK?