It's the same photon but, in this context, it's part of a "back of the envelope" type calculation based on energy quantization ($E=hf=\hbar \omega$) and the assumption that each sufficiently small interval of the energy spectrum $U_\omega\mathrm d\omega$ consists of a number of "equivalent photons" $N_\omega$. It's probably a good approximation but it isn't the modern quantum field theory approach where the Number operator is defined in terms of the Hamiltonian/Energy operator and creation and annihilation operators.
The section on the "virtual photon" is in chapter 18. Section 3 "The Virtual Photon Concept"
The energy of the electromagnetic wave is (in terms of its Fourier components) is calculated.
$$U= \int_0^\infty U_\omega\mathrm d\omega$$
$$U_\omega
=\frac{2}{\pi} \frac{e^2}{4\pi \epsilon_0 u} \ln\left(\frac{\gamma u}{\omega b_{min}}\right),$$
where $u$ is the velocity.
The number of "equivalent photons" $N_\omega$ is defined by $U_\omega\mathrm d\omega = \hbar \omega N_\omega\mathrm d\omega$ such that
$$N_\omega\mathrm d\omega
= \frac{2\alpha}{\pi} \ln(E/A\hbar\omega) \frac{\mathrm d\omega}{\omega}$$
and
$$N_\omega\mathrm
= \frac{2\alpha}{\pi} \ln(E/A\hbar\omega) \frac{\mathrm 1}{\omega}.$$
$\alpha$ is the fine structure constant, $A$ is a numerical constant and $E$ is the energy of the particle.
Hence the spectrum of “equivalent photons” varies approximately as
$l/\omega$. The number of equivalent photons per electron is small, namely,
of the order of 1/137. Equation (18-38) is very useful in relating the
probability of processes induced by electrons, or by other particles
which act essentially only through their electromagnetic field, to the
probability of processes induced by electromagnetic radiation.
