I agree with all of the above to be careful. Very careful. The fact that he suggested (as I read it) that you should meet him at a (probably) deserted resevoir (given it is Sunday between 8 and 9 am) where he's going to have a truck.... plus the phone # thing... scary.
BUT I'm also with Gut in that he may just be a dating klutz...long out of practice. I'm assuming here that you are single, his sister knows it, and that she had your unlisted #, and maybe didn't even know it was unlisted--or if she did figured if you gave him your cell what was the difference.
I'm not sure what the next step should be... maybe the facebook challenge is the right way to go. Although if you are in touch with the sister I guess I'd ask if he got the # from her. Getting that # is the creepiest thing, and if it has an innocent explanation a lot of the rest goes away. However, even if he was thinking that a resevoir walk with is dog would be a nice low pressure way to reconnect in a pretty place, I'd not meet him except in public.