This is one trite, simplistic and fundamentally mendacious way of phrasing what is in reality a complex adaptive nutritional question that isn't so easily dismissed. People have been consuming animal dairy for many thousands of years. These foods are profoundly useful, and have been since around the dawn of civilization for good reasons.
I don't want to enter a battle of reference, but let's agree it's not so "clear":
> The oldest evidence of the production of soy milk is a Chinese mural carved into a stone tablet. It shows a kitchen scene, proving that soya milk and tofu were produced in China in the period 25-220 AD.
Soy milk is a byproduct of tofu, which is not fundamentally more difficult to produce than cheese and others animal milks products. It can even be made without tofu: grind some seed and let them soak in water. I'm not an expert on ancient technologies but it doesn't seem more complicated than taming a squeezing the nipples of a wild animal.
I mean, your own reference says in the very first line, "The earliest record of soybean milk is on a stone slab of the Eastern Han dynasty unearthed in China, on which is engraved the situation of making soy milk in ancient kitchens."
Following the link to the Eastern Han Dynasty shows its timeline to be between 25–220 AD, which supports the saying of "thousands of years" by the skin of its teeth, so you saying their statement is bullshit is disproved by the rest of your own statement.