Websites bounce around all the time. Like I have a client who if I check the keyword at work shows position#1 but when I check at home Position#4. After a couple days from home it's #1 then at work it's #4... work and home are only 20 minute drive from each other, and home is closer to actual client business location.
To be honest I've used various tools showing different positions, I think Google just likes to bounce you around a fair bit, especially when you are updating your site regularly. The more dormant your site the more stable your rankings I think. I don't believe pinging would have anything to do with it but I'm not a Google employee so I don't know for sure.