It's an Atom, just one that's been rebaged to a Celeron. The performance is absolutely terrible and even a cheap i3 would beat it hands-down! It's a shame Intel have diluted their product range like this as it leads to confusion (as you've demonstrated).
Dual-core Pentiums and Celerons (in the vein of those since the Wolfdale days) are still made, of course, and these days are merely cut-down i3s. The Atom-based Pentium and Celerons are a relatively new invention and the easy way to spot them is to see whether they're advertised as quad-core or not; quad-core Pentiums and Celerons are just beefier Atoms.