The engined were running at touchdown, at what appeared to be normal rpm.
AFAIK foaming of runways does not occur in NZ, for two reasons (that I know of): If the RFS use up the HFFF by applying it to the touchdown zone (there is rarely enough to do the entire runway) it takes time to refill the tanks. In that time any fire or spark suppressing effect of the liquid applied will have decreased significantly. HFFF doesn't actually stay "foamy" very long, its effectiveness on runways is considered to be limited, at best. It's best applied, as it was in this case, after the aircraft is stopped, to prevent/contain a post-crash fire.
According to a post re the same incident on the D&G forum, the fuselage is reinforced at the prop line, and no windows directly in line with them.