If unconvinced, try the same with a piece of old sofa, fake leather or vinyl flooring (with or without paint).
I don't think you're listening to what I'm saying about the common air temperature around small fires (auto-ignition of hot gasses at ~600°C is common) and the melting temperature of the binder in these bricks (150°C max).
It's not about ignition of the PE, its about cohesion of the brick PE binder (and thus the sand) at higher temperatures. Your painting this brick that will lose cohesion will do exactly nothing for the performance of the brick.
I dare you to think about it critically, instead of making useless dares that don't address what the other person is saying.
I mean, yes, it's nowhere near western building codes, and if there is a non-trivial fire, you need to get out, fast. Much faster than with most typical building materials, though the bricks won't come loose instantly, and that has to do with thermal mass, conductivity, temperature and amount of heat.
Note, a match will not do, if painted. A blast furnace will, but I do not see the relevance.
Yes, I may have overestimated how much fire the bricks might survive, in my first comment, but I'm not saying the building would withstand a fire - the main point is, that it's more resistant than EPS cladding, couches and PVC flooring, so not as dangerous as it might seem.
again, far before a fire reaches a point where it's widespread the heat of the gasses created by a small fire are already 4x what these bricks can stand before the binder involves melt.
So long before you're worried about thermal mass, there would be nothing holding these bricks together and you have a mass of loose sand and melted plastic.
You could paint it with intumescent paint but I doubt it would be effective given the low melting temperature, and would probably end up costing as much or more as the brick.