How does the Catholic Church explain the omission of identity of the young man referred to in Mk 14:51?
Yes there are several interpretations as to who this young man may have been. The Church offers no definitive answer to this equation.
Being a Catholic all my life and having been in a Catholic seminary for four years, I can confirm that the majority of Catholic theologians consider the young man to be St. Mark himself.
When one of Jesus’ followers (“a certain young man”) is captured at the same time Jesus is being arrested (in Mark 14:51-52), but then leaves his garment behind as he escapes naked, Pakaluk is able to make sense of the strange detail.
“It seems that this young man is Mark himself,” he writes. “It is a detail too small to include otherwise, and it seems unlikely that anyone else would have noticed it in the darkness and confusion. The telling of the incident has a humorous tone of self-congratulation, which is difficult to account for if it is someone other than Mark.”
Can you imagine if you had been the follower of Jesus who was apprehended at the same time as him, but then slipped away from your captors by wriggling free of your clothes? No doubt you would be wryly retelling that unique story for the rest of your life.
Pakaluk notes how the episode is only self-congratulatory for Mark in the same way that Peter ironically notes his own shortcomings: “The detail is humorous, and if written by Mark, self-depreciating.” - St. Peter’s memoirs: a vivid take on a familiar Gospel (The BC Catholic)
The Betrayal of Christ, with a soldier in pursuit of Mark the Evangelist