Well, that is completely normal, your dog just misses you! My Pomeranian does this same thing and at first I thought my dog had a bad memory or something. When I would go out to get the mail and came back in she would act like she hadn't seen me in days.
But I researched it and I found that this is completely normal! After a long day at work you dog has missed you, right? So your dog is just giving you a token to show how much he loves and misses you. Your dog thinks of you as their master and he is giving a gift of love. Isn't it amazing how much your dog understands!?
So in conclusion, don't worry if you see after a short period of time out of the house your dog greets you as if you had gone out on a vacation for a week. Dogs are loving animals they can get very close with you if you let them! Is it just me or do you just adore those little K-9s!