Considering how casual he is, I can think of two possible explanations:
1) Jurassic-Park-style revived dinosaurs have been successfully caught and tamed (or at least, taught that humans are harder to catch than the butchered meat they provide). This man is the zookeeper responsible for them, and they've gathered around him in the hopes that he's brought more food.
2) The man is an experienced time-traveller, and his casualness is held only until the perfect moment to run, leaving the dinosaurs entangling each other.
(He is, of course, from roughly our time; his clothes give him away.)