The first is that I have a common nickname @gmail.com. There are many other users with some variation on that nickname @gmail.com, and people are careless about typos, including suffixes, etc. It's a similar cause to the article, but the username instead of the domain.
The second case is a more interesting one:
I bought an expired domain.
Now I get all kinds of email sent to what used to be legitimate email addresses of the old domain owners. For more than one of them it was clearly their primary email address. I was getting emails related to bank accounts, Netflix, Facebook, etc. I thought about trying to get in touch with those users, but ultimately decided to bounce their email.
It was something I hadn't considered when buying an expired domain, or about my own email addresses, but it's a real problem. Here's hoping my email provider never lets their domain expire.