Thanks for the reassurance everyone, and looks like I can tell them their dog likes me more than them. 
Twice I’ve had dogs I was petting react to me like that, and both times the groomer had cut them near their ears, and I was inadvertantly hurting them when I touched the area. The Chow liked to have took my arm off, only time I’ve ever been bitten.
Another vote for the canine grin. It’s actually pretty common, and doesn’t seem to be breed-specific. Never actually seen a Lab do it, but I’ve known border collies and Aussies that were smilers. I think it’s something they pick up from humans. My late Siberian Husky, Bandit, OTOH was a laugher like this one. Big, bright-eyed, open-mouth happy face, usually accompanied by that characteristic Husky comment; “woo OOO ooo!”(Huskies don’t bark much, but they’re fairly vocal anyway).
James Herriot, the English Veterinarian who wrote the *All Creatures Great & Small *series made mention of canine “smilers”, particularly a Yorkshire Terrier named Victoria who “parked herself at my feet gazing up at me and repeatedly baring her teeth in an ingratiating grin”. I think this is the first place I heard of it. When I read that part I was reminded of dogs I’d met, whom I’d thought were hostile but were actually favoring me with a friendly smile.
SS
Labs are ‘mouthy’ in my experience. I put it down to being retrievers, they’re accustomed to opening their mouth in excitement.
My non-lab dog was a starer. Some people regard that as aggressive but that was them anthropomorphizing her. (She just liked to stare and wiggle her eyebrows when I talked to her. )
I had a Kelpie who smiled all the time. He would even do it on command. The first time I saw him do it, he was ten weeks old and had just spent his first night in our household. He slept in the lounge room by himself all night, and I guess he was crazy happy to see us in the morning, so he stumbled out of his little bed with those oversized legs of his and grinned the biggest grin. That was the moment he won my heart forever.