I queried an agent with an idea for a biography. The agent's assistant replied that my idea was too close to an idea that she (the agent) was discussing with an author. The other potential project was a biography of a different person, but apparently the theme is too similar to mine (of course, they didn't give me details about who the other biography was about).
So, is this a boilerplate rejection, without particular significance, or does it indicate cause for optimism that my idea is similar to one which an agent is actively contemplating? Or is it bad news that it might suck the oxygen out of the room for my idea? If you have any thoughts I would be flattered to learn them.
There's no way to know whether this was a genteel pass rather than "holy moly you think you can write, what the everloving duck is this mess."
Nor can you let it guide you in further querying or any assessments of the validity of your project.
All you know for sure is this particular agent passed. That is all you know, and really all you need to know.
However, my eyebrows did go up at the phrase "idea for a biography" because querying ideas is a really bad approach.
A good query for a biography (or any narrative non-fiction) is a lot more than just an idea. It includes an overview that talks about the subject of the biography, the significance of the proposed book, what new information you'll include, or what new interpretations of existing information you'll offer. It includes why you are qualified to write the book, and an assessment of previous books about the subject.
In other words, it's not an idea, it's a well thought out offering.
I can't tell you the number of queries I've gotten for very abstract ideas, from people who think they're qualified to write about something cause they're interested in the topic. My favorite is still the gent from west of nowhere who wanted to write a book explaining the existence of god.
Bottom line: the only thing you know about a rejection from an agent is that it's a pass. Don't try to parse out anything more. There are too many variables in play to draw any kind of reliable conclusion.