Mastodon CEO Eugen Rochko was asked about Elon Musk's takeover of Twitter during an interview.
He said Musk "is not entirely comprehensible" and must now "deal with the fallout" of his purchase.
Rochko's comments come as some Twitter users migrate to Mastodon, which just hit 1 million users.
Eugen Rochko, the CEO and founder of Twitter rival Mastodon, criticized Elon Musk during an interview with Time Magazine that was published Sunday.
When asked what he thought of the Musk's takeover, Rochko said that "the man is not entirely comprehensible" and that he doesn't agree with a lot of his recent behavior. He called Musk's purchase of the platform an "impulse decision that he soon regretted," and that the billionaire must now "deal with the fallout."
Rochko also disagrees with what he described as Musk's "absolutist" stance on free speech, saying that his desire to open up the platform to the "most intolerant voices" will not lead to open debate, but a "cesspit of hate."
Mastodon has seen a surge in growth since Musk purchased Twitter, though it's still small in comparison. As of today, Mastodon has reached more than 1 million active users and registered nearly 480,000 new users since October 27th, according to Rochko. Twitter has around 237 million total users.
The major difference between the platforms is that Mastodon is a decentralized platform created by a crowdfunded nonprofit, meaning that no one person is in complete control. Users are required to join servers specific to a city, country, or interest like gaming, and each server is moderated by its owners, who can delete posts that include hate speech or illegal content.
Some Twitter users have voiced interest in Mastodon in the wake of Elon Musk's purchase and concerns over how strict or hands-off he'll be with content moderation. In May, Musk said that he would reverse former President Trump's account ban if he purchased Twitter, though he's since said any decision on reversing suspended or banned accounts is weeks away.
But there are signs that some Twitters users have been emboldened by Musk's takeover to test the limits of its content moderation. In the days after Musk officially took over, online trolls flooded Twitter with more than 50,000 tweets containing the "N-word" and other forms of hate speech.
On Sunday night, Musk ordered Twitter to permanently suspend accounts if they engage in "impersonation" shortly after the platform reportedly suspended several celebrities and high-profile Twitter users like Kathy Griffin and actor Rich Sommer for mimicking Musk with their profiles.