Is touching a girl's lower back not a bit invasive/flirtatious/sexual/forward?

i had a guy that I don't really know that well who is a server at a restaurant come up behind me in the restaurant and place his hand on my lower back and lean in and ask what he could help me with...

just wondering from other girls - would this surprise you? from guys - would you do this to a random girl? and from everyone - is this... normal in the united states (I am an immigrant from Israel and the social norms there really aren't different from the US and so here I'm thinking "this is not exactly appropriate", and then wondering if maybe its just something american men do?)