Yes, it looks like Grey mould, Botrytis cinerea.
It’s a fungus brought on by damp and heat.
June to September is traditionally the time of more moisture in the air, although it doesn’t seem like it.
This time of year I use an anti fungal (I’m a carpet cleaner) as the humidity can encourage the growth in a very short space of time.
Ventilation is the answer really, thinning out.