Not exactly... I believe "pad" is generated by some kind of a script... maybe one of the python scripts... I wouldn't really call it a part. It generates one connector (connector0pad) in the PCB view.
A Part generally consist of 4 files (part.fzp, part_breadboard.svg, part_schematic.svg, and part_pcb.svg). There are a lot of tags that can be uses in the .fzp to allow the part to do things like allow it to rotate or flip or not to rotate or flip... among other things. I just don't know what they all are. There may be one to allow the part to be sizable... maybe, maybe not, I just don't know what it would be. I tried a bunch of experiments one time, like "size, sizable, (true), etc.". I couldn't fine anything that would work. Maybe one of the core people can answer that question...
A part .fzpz in just a zip file. You and unzip it to get a better understanding on how they work...