That's a gross exaggeration. If you own 0.1% of the company, you're likely to be diluted to around 0.02% at the very worst, and most likely 0.04% or so assuming 3 rounds of funding.
That's assuming a positive outcome that clears preferences of course - if the company goes in a fire sale you're not going to make anything at all. But assuming a billion dollar exit means you're assuming not a fire sale.