Probably a little of both. I'm hesitant to say without actually seeing the behavior. Dogs are social animals; they want to be with the pack, and part of being in a pack is watching out for each other (Have you seen Ice Age?); that's why they get along so well with humans - we live in "packs" too - families, communities... and we take care of each other. He's also keeping that eye on you to learn about you and your cues (as I mentioned previously).

Overly protective and/or separation anxiety behaviors have telltale traits.

Separation anxiety can occur if/when owners make a big fuss over comings & goings. (Spoze you were a little kid and your family got you all worked up like you were going out to have fun, then slammed the door and left you alone for several hours. Same when they got home and you wondered what you missed. It's not that bad, but...) Dogs with SA can also get destructive because they're basically frustrated and have little other outlet.

Protectiveness is usually more a show of aggression if anyone comes within what the dog perceives as its territory. Unfortunately the anyone can sometimes be another family member.

Either behavior should be corrected/dealt with. I hate to go into particulars, because it can get a little controversial with different theories - almost like childrearing. There's a lot of information online and in books, but again - good & bad, like everything else.

Doc