At my son's school there is a retired police officer who lives just down the street. He walks over and watches the entire morning routine every day (buses coming in, parents dropping off). This is apparently something he arranged with the school. He has a direct line to the police hotline for any trouble at schools, so he's just one more set of eyes. Trained eyes. He volunteers his time, and he provides a pretty good service. In addition to being a direct line to the police, he's always there, everyone knows it, and so that's a deterrent in itself.
So, before coming to the conclusion that it's shady behaviour, check it out. Please understand, I'm not criticising your reaction whatsoever. The entirely natural reaction to situations involving your children is to be protective. Well done, you're being a parent. That gut reaction can lead to unfortunate situations, so we all need to exercise caution.
I'm really hoping old dude in front of your daughter's school is doing something awesome.