I asked Evan Williams, Twitter co-founder and board member, what he thought of the news. His answer? User count is the wrong metric to focus on.

In his words:

It’s a question of breadth versus depth. Why is users the only thing we talk about? The crazy thing: Facebook has done an amazing job of establishing that as the metric for Wall Street. No one ever talks about, ‘What is a [monthly active user]?’ I believe it’s the case that if you use Facebook Connect—if you use an app that you logged into with Facebook Connect—you’re considered a Facebook user whether or not you ever launched the Facebook app or went to Facebook.com. So what does that mean? It’s become so abstract to be meaningless. Something you did caused some data in their servers to be recorded for the month. So I think we’re on the wrong path.

If you think about the impact Twitter has on the world versus Instagram, it’s pretty significant. It’s at least apples to oranges. Twitter is what we wanted it to be. It’s this realtime information network where everything in the world that happens on Twitter—important stuff breaks on Twitter and world leaders have conversations on Twitter. If that’s happening, I frankly don’t give a shit if Instagram has more people looking at pretty pictures.

I noted that Wall Street certainly cares about other things.

Williams said he isn’t authorized to comment on anything financial, but countered that Twitter’s monetization has been going very well. “Twitter makes a hell of a lot more money than Instagram, if that’s what Wall Street cares about,” he said.

Regarding Facebook’s method for counting users, Williams is correct. According to an SEC filing, Facebook’s definition of an active user includes anyone who “took an action to share content or activity with his or her Facebook friends or connections via a third-party website or application that is integrated with Facebook.” So even if you don’t go to Facebook for a month, you count as a monthly active user if you use an app which you have signed up for with your Facebook account and shared something. [Note: This sentence has been updated to include the words “and shared something” after a Facebook representative clarified that a user must actually share an activity to Facebook to count as “active.” If a user “likes” something on a third party site, or listens to a Spotify song which is then automatically shared to Facebook, that counts.]

To that end, Twitter is opening up its own definition of its user base. Last month Twitter CEO Dick Costolo revealed that content posted to Twitter actually reaches 500 million people each month when you take into account anyone who has seen a Tweet embedded in a webpage or another app. The takeaway? When it comes to the horse race for users, Costolo doesn’t give a…well, you know.