It is not technically true. For one, the question didn't say "in Earth's atmosphere." But more importantly, if you get a kilogram of steel and a kilogram of feathers and put them on a consumer-grade scale on the planet Earth at standard temperature and pressure, they'll both show the same reading. If you are a person that needs a specific enough scientific answer to account for any ridiculously minuscule effect caused by the environment, you aren't asking it in such an off-handed way.
If I asked "does ice float?" and got the answer "Ice floats on liquid water." that would be satisfactory. If I got the answer "Ice floats on liquid water if the ice is composed of hydrogen-1 atoms, or if it is placed in water composed of the same (or heavier) hydrogen isotopes." I would be dissatisfied because that's a confusing answer that nobody is reasonably looking for.