Start with the fact that for a given aircraft at a given weight the stalling speed is a constant EAS.

The reason "below 10,000ft altitude" is added to the confusion soup is that compressibility cuts in and IAS diverges from EAS above this height, so stall speed is higher in IAS than in EAS.

The same factor, rho, that is used in calculting lift is used in calculating EAS/IAS, so changes in altitude and temperature, that affect density, and density itself don't affect the accuracy of the statement at the top.

But we all agree that the heavier the aircraft the higher the stall speed.