I’m not sure what was used in that particular case, as these are just from the Starling demo, and were probably created for use in AS3 years ago by Daniel Sperl, the original creator of Starling.
Don’t worry though, because creating it again is certainly possible. I use TexturePacker 6.0.1 (the last version to support the ATF format), which I provided details to here:
I’ve been using this for years, with a lifetime license. I haven’t explored options (haven’t needed to), but there may be other alternatives now.