Probably a misunderstanding of the concept of normalizing units to '1' so that, for example, the speed of light is is simply unity instead of arbitrary Terran units like 299 792 458 m/s or 186 282 miles/s.

There's a few ways of doing this: https://en.wikipedia.org/wiki/Natural_units

Alternatively, and more likely, it's based on the "relative" strengths of the different forces, where ratios of about 10^40 do tend to turn up.

For example, the ratio of electric force versus gravitational attractive forces for a proton and an electron is 2.3 x 10^39 which is close.

PS: A fun thing to numerological coincidence to consider is that 2^128 is about 3.4 * 10^38, which is weirdly close. It's almost like gravity is "rounding error" on a universe simulator made with 128-bit CPUs. Similarly, 2^256 is close to the Eddington number of ~10^80, which is the estimated number of particles in the Universe...