What has likely happened is that a mass-brute-force attempt to access accounts took place.
There is also the high potential that given the huge number of security breaches (especially in the gaming world) that the hackers are attempting to login with email addresses and rainbow-tabled passwords from previous breaches with other organisations.
As this only affects some accounts it is highly likely that your email address is either publicly available or was leaked in a security breach.
For many people with email addresses like
jimmyluvs2bl0w@gmail.com, their password is much more likely to be correctly discovered than the email address itself as people tend to be lazy and use common passwords, but owing to everyone needing a unique email address these are not guessable.
If you have something like Gmail my recommendation to you is to use the '+' feature for everywhere you are signed up to. For example
jummyluvs2bl0w+psn@gmail.com, and of course always use a unique password.
If PSN was hacked again they'd only have your PSN email address, and can therefore not get into your PayPal account or whatever they might try.