Technical it is not impossible. I give the example of the vivitek qumi q8, okay without battery, 24p 1920x1080 AND 1000 ANSI lumen, stated on their site. And the power consumption is the same, about 60watt.
I think my picopix max one will also have only 350 ansi lumen. I was also thinking it was 850 ansi lumen and not led-lumen ( the eye has ‘the perception’ that it is brighter because the colours are more pure than a lamp based projector with colour wheel.
Bot to be honest, i had also a qumi projector ( quni q3plus) with 350 ansi lumen and they drived the leds too hard so the green led turned yellow. For long living maybe it is not technically possible to make such extremely powerfull projector without cooking the inside and prematurely aging the leds.
In my home i have a professional led projectoe ( hitachi) with the philips hld-led inside ( a blue led array activated a green fosfor rod). But that machine weighting 15 kg, has 3 big heatpipe coolers and is much bigger. So maybe i know the intention was to have it 850 ansi lumen, but after awile there were maybe problems with life expectancy or the cooling… Or with the available leds. We will not know exactly why this changed. You can read more about led lumen and ansi lumen on projectorcentral 
. Hope it helps a little bit…
It doesn’t matter if there were problems or not - they made a fraud, lied to everyone and sold (and keep selling) a product that is at completely different pricepoint. Projectors with around 350 ANSI lumens cost 50-60% as much as PPX620.
And yes, perhaps it was not possible to create a projector with such brightness in such a small factor with battery included.
Xgimi has recently released Elfin model, with pretty much identical form factor, has 850 ANSI Lumen brightness, costs 25-30% less than ppx620, though it doesn’t have a battery built-in. But Xgimi halo plus does have 900 ANSI lumen and a built in battery, and costs just slightly more than ppx620. Yet it does have Android 10/11. Yes, it’s larger and heavier, but it’s much better option.
Screeneo are fraud company.