I have seen a few Lexus Ct200h's for sale on Autotrader, which do seem to have a lot of white dust/particles in the cabins spread across the seats, steering wheel and so on. The particles are whiter than the dust and pretty round.
2016 Red Lexus CT Hatchback 200h 1.8 F-Sport 5dr CVT Auto for sale for £15,834 (autotrader.co.uk)
2015 Multicolour Lexus CT Hatchback 200h 1.8 Advance Plus 5dr CVT Auto for sale for £15,226 (autotrader.co.uk)
2016 Silver Lexus CT 200h 1.8 Luxury CVT Euro 6 (s/s) 5dr for sale for £15,990 in Chester, Cheshire (autotrader.co.uk)
Have a careful look through the pictures of the 3 cars I listed. They all seem to have the white powder/particles in the cabin. This is probably a thing in the UK.
Some say it is calcium carbonate, and some say it is aluminium oxide.