It's a humorous reference to my self-aggrandising online personality (which is why I use it as the tagline of my blog). In a sense, given that modesty is downplaying one's own abilities and achievements, it is indeed lying.

It's a (not at all serious) possible "righteous justification" of complete immodesty, which appealed to me. It was something I said spontaneously a number of years ago when Lauren rightly accused me of lacking modesty, and the phrase stuck.