The idea that they really send spam to validate an email address sounds to insane to be believable.

Is it possible that they are somehow leaking the address to actual spammers?

For example, they (or the hypothetical email validation SaaS) use an infected email validation library that ex-fills every email supplied to it, or something like this.

Yeah. The abundance of comments that take the article at face value makes me pause. I assumed it was satire.