^ that quote seems to refer to entering Laos coming from China, not going into China from Laos. Laos is quite easily do-able on vehicles from abroad.
At gt-rider dot com I read about a guy, who did manage to sneak into China from Laos a couple years ago, and he toured many southern parts of the country. But there was one drawback - he was on a Chinese-registered bike, that he´d been able to buy from somewhere in Thailand.
And even if you managed to find a bike like that, there´s no guarantee the same would still work, or that it would work for you. It is not the ´official´ way, where you´ll be assigned a guide, and pay big money.