You've got to go with your initial gut response. They were looking at your stand, showed interest in your camera, were on posted property, avoided driving by you when it was obviously easier, etc.

I agree with texastracker, they will be back.

I'd take my stuff down and move it or take it home. You really don't need the camera up this close to the season and the stand you can put up early on Sat.

I'd suggest spending a little more time on site at odd times just to let people know that someones watching.