How to choose a MOSFET with as low Vgs as possible?
The number is correct, but the designation (at whatever distributor site- looks like Digikey) is wrong- it is 400mV minimum. You can't really trust such info (even) as much as datasheets (which also contain errors from time-to-time). 



Vgs(th) is best used as an indication of where the MOSFET will be mostly 'off' so the minimum is usually of more interest than the maximum. 

As far as finding a part that meets your specifications, you can use the imperfect sites and try to verify the data by looking at the datasheets one by one. I don't know of any better way. 

By the way, if you're interested in particular in extremely low Vgs(th), you can use depletion mode transistors, where the voltage is actually negative, or you could consider boutique parts from ALD which are tweaked to have 0V +/-10mV Vgs(th).