you think he should ve waited for invitation?
well, there are different kinds of invitations/greetings:
1. We will be very happy if you visit us
2. Yeah, you can visit us
3. Your visit is due
4. abay idharr aaa
5. Who? Oh yeah, please come in
6. Who? Here again?
I am sure there are more, but this visit is covered by some in the list :D