Rare events do not arrive evenly
Even a genuinely excellent finisher converts a modest share of the chances he gets, which means a run of games without a goal is well within ordinary variance rather than automatic evidence that something is wrong. Rare events cluster and gap unevenly over any span of games short enough for a season to actually contain, and hockey's scoring rate makes those gaps common.
Treating every quiet week as a crisis assumes scoring should arrive smoothly, and it does not, for the same statistical reason that a fair coin can still produce a run of five tails in a row without the coin being unfair.
Watch the chances, not the ledger
The more useful question during a drought is whether the player is still generating and being involved in good chances at his usual rate. A player doing everything right and getting stopped by good goaltending or bad luck is in a completely different situation from a player who has stopped getting to the same spots on the ice, even though both show identical zeros on the scoresheet.
That distinction requires actually watching the shifts rather than reading the totals, which is more effort than checking a box score, and probably why the lazier explanation — he is slumping — gets reached for first.
What the word assumes that may not be true
Slump implies a cause: confidence, mechanics, something wrong that needs fixing. Sometimes that is accurate. Often the accurate description is simply variance operating on a low-probability event, which will resolve itself with no intervention required beyond continuing to generate the same chances and waiting for the rate to catch up with itself.
I would rather withhold the word until the underlying process actually looks different, and in most cases I have watched closely, it does not. The goals just have not landed yet, which is a far less dramatic sentence than the one usually written about it.