Just got my PB a couple days ago so it forced me to update to the latest version before I could do anything so i know I had whatever the latest public release was, .358 i think. Last night I had an update come in, it was like 64-67MB or something, when the PB rebooted I didn't notice anything and version number stayed the same.
You might have received an update because perhaps something either got corrupted and needed to be replaced or if you deleted some programs it just re-downloaded them.
Where'd you get it? Just thinking that if you picked it up in Canada and then brought it home to the States, maybe that would account for the second small update. As an example, the Video Store isn't available in Canada, but it is in the US.