Maybe there's a missing "may" in there, but there's another possibility.
If you encounter the card under circumstances that don't allow you to evade it, then you would move on to the check to defeat, and the scenario probably wants that card to end up displayed next to the scenario rather than banished back to the box after it's dealt with. Adding the two words "or defeat" to the first power handles possible exceptions, and it's not like the card is short on available space for printing extra words.
Even if the scenario that uses the Elusive Knowledge Henchman doesn't include that possibility, the wording also future-proofs similar cards that may be built in a hurry using Elusive Knowledge as a template. It's better that we have a discussion at our leisure about redundant text during the Season of Factions' Favor than a game night comes to a halt on a technicality during the Season of the Great Taldan Bake Off.