If there was a central forex exchange, then that huge liquidity would be applicable. Instead, retail forex is only a tiny fraction of the daily exchanges in the forex market. I've seen a video showing how during very quiet times of the marker, a single lot bought or sold can move the market by a pip.
Add in that unethical brokers are more than willing to move the market by several pips for their own benefit, and the bragging about virtually unlimited liquidity preventing market manipulation falls flat.
By the way, your text appears to be quoted from dailyfx.com/forex_forum/community-section/630473-advantages-currencies-over-stocks.html
Are you the original author?