Is this a massive security issue?

so, after an epic hard drive fail, i formatted a usb stick and installed mavericks onto the stick. popped the stick in and booted from that, then using a large portable hard drive i plugged in, i accessed all the files on the mac book and copied them to the portable hard drive and then rebooted and reinstalled mavericks onto the mac and then copied all the filed from the portable to the mac.

so....

can i now plug my usb into any mac book, reboot and then just access all the files on the hard drive willy nilly? i seem to only have to type my password when deleting files from the system / library folders... documents wasn't requesting anything.