<PERSON> is equating the different length scales associated.
In quantum mechanics, the characteristic length scale is decided by the mass of the particle. It is known as Compton wavelength ($\lambda_c$), and roughly speaking, it sets the length scale where relativistic quantum field theory becomes important for the description of physics; because if you try to localize a particle such that the uncertainty in position is smaller than $\lambda_c$, the the uncertainty in momentum becomes high enough to (from $E^2 = m^2 c^4 + p^2 c^2$) induce uncertainty in energy of the order of the mass of the particle. This means that at such small length scales, and equivalently, high energy/momentum scales, we must take special relativity and particle production/annihilation into account. 976
The Compton wavelength is given by:
$$\lambda_c = \frac{\hbar}{mc}$$
In general relativity, the characteristic length scale is also decided by mass, but is directly proportional to it. It is known as Schwarzschild radius $r_S$. The event horizon of a static and spherically symmetric object lies at $r=r_s$ and is given by:
$$r_s = \frac{2 G m}{c^2}$$
Substituting $r_s$ for $\lambda_c$ and barring a factor of $\sqrt{2}$, we can write the characteristic mass scale for such a situation in terms of the three fundamental constants of the three fundamental theories: $c$ of special relativity, $G$ of general relativity and $\hbar$ of quantum mechanics, and it is known as Planck mass:
$$m_p = \sqrt{\frac{\hbar c}{G}}$$
So the Schwarzschild radius of a black hole of mass equal to the Planck mass is its Compton wavelength.
The number of microscopic states of a black hole with given macroscopic characteristics (like charge, mass and angular momentum) can be written in terms of the area $A$ of the event horizon. This is known as black hole entropy and is given by:
$$S = \frac{kAc^3}{4G\hbar}$$
where $k$ is the <PERSON>'s constant.
The issue that black holes are not entirely 'black' and end up radiating because of particle production when quantum mechanics is involved has led to many debates and open questions that fall under the umbrella term of black hole information paradox. 688