Yes, this was an oversight and I'm glad you wrote in so we can tackle the sticky topic of who versus whom.
This grammar issue is one that seems to invite the most divided response. Some are rabid about correct usage regardless of how it changes the tone of the sentence and others simply avoid using whom at all costs. These latter folks aren't alone. In his column “On Language" in The New York Times Magazine, William Safire wrote:
The best rule for dealing with who versus whom is this: Whenever whom is required, recast the sentence. This keeps a huge section of the hard disk of your mind available for baseball averages.
Linguists and observers of language have been predicting the disappearance of whom since the late1800s. But it's still around and we all might as well know how and when to use it.
Here's the short answer: Use who when the pronoun acts as a subject. Use whom when it acts as an object. Maybe that just confuses things further. Let's back up.
The subject of a sentence is the person, object or place that is doing the action:
Leslie hit the ball twice.
Denver is beautiful.
The object is acted upon.
Fran slammed the door.
I loathe you.
So, use who when you're replacing the subject of the sentence:
Who hit the ball twice?
Use whom when replacing the object of the sentence:
You loathe whom?
When sentences get more complex, remember that you're looking for the pronoun's role—as subject or object—within the clause. The italicized phrase below is the clause:
Freddy feels like a marathon runner who finally crossed the finish line.
In the clause, the pronoun takes the place of the subject, Freddy.
A final piece of advice: always double-check your usage for careless mistakes. Thanks to this close reader for keeping me on my toes.