I saw reports of this on the TV, weren't these houses (which are described as "terraced" in this report) temporary gerry-built ones? IE, far more vulnerable to a fire suddenly taking hold than your average terraced house?
Normally I'd say of course it's reasonable to be in the garden. In a house which is made of straw though, I guess being in a different room is dangerous. Or being in the house at all.
I know nothing of fires so have no idea how quickly one can take hold given a certain mixture of materials. I presume that house had no smoke alarms?