"Came across" vs "comes across" [closed]

What's the difference between "came across" and "comes across" when used in the following sentence? Are both correct?

Steve Irwin tells the story of a boy who was walking through a swamp when he [came | comes] across a crocodile. The boy was trying to get home, but the crocodile started following him ...

"... came across" is clearly correct, merely another clause in a sequence describing past events.

in "comes across", the change of tense transfers the mind of the reader from the present, as they read about a series of past events, to the instant in the past when important things happened. The change attempts to put the reader into the circumstances as they appeared at that instant.

"... a boy was walking through a swamp, when he comes across a crocodile ..." does this effectively. We transfer from an comfortable armchair read to suddenly experiencing the perilous event as immediate and pressing.

From that perspective, "comes across" is correct. I, not being a creative writer, expected the present tense to continue in the following prose. It does not, as if Irwin then wants to relax the reader.