When approached, a Sony Computer Entertainment America spokesperson provided Joystiq with this statement: "While we don't disclose the exact criteria used, we can say that select active PSN users were chosen to receive an XMB message that included a credit for their SEN [Sony Entertainment Network] Wallet as part of this special promotion."
It should be noted SCEA's Morgan Haro provided the same statement when asked about last month's credit giveaway. However, unlike previously, this time the XMB message makes no mention of loyalty. So it's unclear if this is a separate rollout from the one last month, or if Sony just wised up to not deeming a select group of its userbase as "loyal." We tease, Sony - free credit is just capital.
[Thanks to everyone who sent this in]