Apologies for this delayed reply. We looked into this new Guest Payments service, and apparently this only makes it optional for the seller (payment recipient) to have a PayPal account, so e.g. if you don't normally accept payments by PayPal but someone insists on sending you a one-off payment through PayPal, you can accept their payment without having to sign up for PayPal yourself.
That blog post's statement, "Guest Payments allows developers to collect credit card payments without requiring their customers to open a PayPal account," is a bit confusing, as "customers" in this case refers to the developer's clients for whom they are building an e-commerce site -- i.e., the developer's "customer" would be the seller, not the buyers who would be shopping on the seller's site. Incidentally, this sort of confusion is why we prefer to use the terms "seller" and "buyer" rather than "customer", "client", etc. in our own communications and help pages. :^)
As for PayPal checkouts offering buyers an option to pay directly with a card rather than logging into or starting a PayPal account, this FAQ page explains more about the conditions (that we're aware of) when PayPal will or won't offer that card-based option: