I cannot find any information to suggest 420 strains of bacteria...
As a matter of fact, they don't list the strains at all on their website.
It simply says "Multiple-strains of probiotic Lactic Acid Bacteria (LAB), Bifido Bacteria, yeast extract and dietary fibre, all in a proprietary formulation."
Many yoghurt starter cultures that can be purchased over the internet contain multiple strains of Lacto and Bifido strains, as well as Strepto (particularly S. thermo- extra good at converting lactose to lactase) strains. There are also many places to get the ultra starters for higher probiotic counts.
This looks like its just a marketing things so it's all available (maker, starter, etc.) from one company on one website.
Basically its just saying that homemade yoghurt is better than store bought... sort of a no brainer. Big companies use minimum cultures and culture times, they add thickeners, flavorings etc., time in processing, packing, shipping, and sitting on the shelves can decrease probiotic counts.
Making homemade yoghurt is great... but I'm not buying the sales pitch that THIS homemade yoghurt is 'better'.
All yoghurt is made via the action of those little cultures reviving, splitting, eating/digesting, and creating their yummy waste until the milk is no longer milk... and that takes a LOT of little beasts, whatever numbers you want to throw at it... 1 trillion, 100 billion...
That's my yoghurt makin 2c.