Kara Danvers/Supergirl's time is limited in episode 4 due to Melissa Benoist's role on Broadway in Beautiful: The Carole King Musical. To accommodate her schedule, season 4 began filming with the fourth and fifth episodes in mid-July. Melissa's run on Broadway did not end until August 4th.
Actor Sam Witwer played officer Davis Bloom in Smallville, a Superman based show. In Smallville he turned into the Kryptonian beast Doomsday
This episode takes place from 2016 to 2018.
The episode title is a pun. "Man of Steel" is of course Superman's nickname, but in this case it refers to Lockwood's father, who worked in a steel factory and triggers his son's anti-alien feelings, as well as Lockwood himself, who fashions his costume out of discarded steel parts.
Sam Witwer and Xander Berkeley worked together previously in Being Human (2011-2014)