Nothing unusual about that.

Can happen if a device is still mining an old block and then submits shares, the shares then get rejected as stale. Presently that seems to account for almost all of the rejected shares on my own rigs, so I'd imagine its the same.

I dont know what the pool difficulty you've been set to but its likely it was only 2 or 3 shares that accounted for the 7000 difference. Its insignificant and perfectly normal.