There are multiple layers of confusion arising partly from the way that snippets of things end up in videos and copied online. You have to read the (copyright) books to get all the info.
First of all UK "flowerpaste" is what we are discussing NOT the fondant that you would use to cover a cake--that fondant is called "sugarpaste" in the UK.
Nicholas Lodge works in the UK where the best eggs come from chickens that have been vaccinated against salmonella. Alan Dunn explains this in HIS flowerpaste recipe.
The closest equivalent in the US and Canada would be eggs from a farm certified to be both "organic" and "free range" that raises its own grain to feed its chickens without any restaurant scraps being added. Not a common combination.
So reconstituted egg white powder (NOT meringue powder) would be the safest version of egg white.
As soon as the petals are bone dry, the microorganisms cannot live in them. This is the same as hard dried royal icing. And just think all you cookie makers, how many times you use royal icing--right?
