Why wasn't I pulled over at any time during my 40 minute drive and do the cops have the right to come on my property to investigate the accusations?

When I got home, safely thankfully, I was in my driveway and just about to exit my vehicle when a cop knocks on my window. I exit and they said someone called that I'd been driving erratically and assumed I was intoxicated. I know my wrong doing but I find it odd three cop cars show up, go through their duties etc. and I'm on my property. I've heard people can get DUI if in their car in public areas, even if they are just sitting g in the drivers set, but on your own property? My drive home consisted of back country roads, cruise control set at 55 and yes I jerked the car once when my phone rand and it startled me.