From the description, it doesn't really seem to be full Tail Call Optimization, but only optimizes tail recursion. At least all the examples are about tail recursion, where the function calls itself in tail position, which can indeed easily be changed to a loop. Tail Call Optimization would mean it optimizes any function call in tail position. Typically you'd implement that with a trampoline, but it doesn't seem like this does that.

Edit: It's actually called out under limitations "No mutual recursion: Only direct self-recursion is optimized"