It's a trick. The verbiage on the page strongly suggests you have to log in, but there is a little link or something to skip it. It has been a while since I bought through paypal, but I always skipped it because it was so much more of a hassle to log in.
No, I think this means PayPal recognizes tptacek's CCs and forces a log in. Even with a new card, perhaps they'll just base it on the name and refuse to process it without an account login.
Even with a new card? Are you sure? That'd be surprising, given the overwhelming duplication of first name/surname combinations.
I think you're referring more to the "jlee" and "rsmith" combos than the "tptacek" ones.
Paypal fairly recently switched from "login encouraged" to "login mandatory".
I bought something this morning without having to login..
If your credit card is in their system then the only option is to login.