Yep, you're right, that's the transparently resizeable array thing, and it's exactly how Java's ArrayList class gives the feel of a resizeable array while it actually manages fixed-size backing arrays for you. That's why I linked the source to that class. :)
It's that or some magic with larger-than-needed arrays that automatically grow by a bunch extra every time they hit their boundary to make appends faster, while blowing up memory use and making append performance unpredictable.
Lots of (especially) scripting language hide this behind automagic and you see tons of append-in-a-loop where it's not really necessary, as a result.
[EDIT] had insert two places I intended append. Me need coffee.