They are right – reed is flammable…
and they are wrong – we live now in times when science is able to turn any flammable stuff into a nonflammable (even fire retardant) material (I strongly hope we are just one step away from inventing the nonflammable safety matches).
In the past, the thatchers solved this problem with dipping the thatching straw into the mud. It formed a hard, nonflammable crust over the thatched roofing so it was quite safe when confronted with some smaller fires (fireplace sparks, etc…).
Nowadays you have much more possibilities how to make your thatched roof fireproof as well.
Following methods of fireproofing your thatch roof are worth your consideration:
Fire retardant sprays for thatched roofing
There are some substances available on the market, like e.g. Flame Stop I-DS, which prevent the spread of flames by developing a chemically self extinguishing reaction.
Most of them are available in the form of an aerosole (spray).
Fireproof aluminum foils
As aluminum is perfectly nonflammable material (it is a metal able to last high temperatures) even a thin foil helps to keep your house interriors thermally separated from the roof (this is the method that doesn´t protect the roofing material itself – let it burn, if fire is its destiny, but rather keeps the other parts of the house separated and so safe from the roof in flames).
Fireproof batts (thatch batts) that are usually used for filling the roof framing spaces between the truss beams. Thatch batts actually are the rockwool batts, again, separating the thatched roofing from another parts of the house.
Do you think none of the above mentioned methods would protect your home enough from fire?
Separately maybe they wouldn´t… but why don´t you combine them? You´ll get one really reliable, water- and fireproof, natural, ecological and cool-looking thatching material that last years and is quickly reparable at low cost.