There's more to the no killing code then simply killing = bad. That's a straw man.
This
has numerous variables to account for which Superman can do and remain faithful to the concept."killing in self defense or defense of others"
This Superman did it humanely, and has a body of work in numerous situations backing him up so it's not his go-to for everything. This is an execution.
This is murder.
Superman's reactions to both are different, as well. He felt massive guilt over the former, over the latter he screamed once and never thought of it again then kept on killing.
This isn't just about killing, it's that killing is the only solution Superman should use to defeat the bad guys. A big problem with Snyder's Superman is that we only know his history by killing people, and being ambivalence about death around him (Lex's goons fighting Batman, being Godzilla in Metropolis) and none of this gets fully explored in any movie by Snyder. Superman's actions are never actually explored as they should, and all he does is pout in response.