He just pointed that out. Not quite sure you understand
why they are understood to be massless, and what that really
means? The kind of mass we're used to dealing with is essentially rest mass, although you're not even quite getting what "mass" is, because you're thinking in terms of what you see around you (which isn't an uncommon mistake, after all).
The picture isn't quite so simple though once you deal with photons and subatomic levels.
Imagine a box made of "perfect" mirrors on the interior, surfaces that reflect everything and absorb nothing. If you were able to trap some photons inside, they would
add to the
rest mass of that box. This is because of special relativity, that says E=mc2 - if you add to the E, you have to add to the M in proportion with the constant C squared. That's what it means.
Add to this the fact that a photon with energy of greater than just over 1 Mev can be converted to an electron-positron pair, each having a mass of just over 0.5ev in the right conditions.
Technically a photon
is energy, it isn't a container for energy or really a thing with energy, it just ...is. Photons are
never at rest (and never have rest mass, the mass with which we are acutely familiar) - but they have nonzero momentum.
Photons behave
as if they have mass when they pass very very large objects - such as galaxies - because they follow the curvature of space-time taking the same path as if they had a tiny mass when they in fact do not. Energy is also capable of curving space-time (in fact, the curvature is really equal to the energy-momentum at that point, if I remember right), so photons
do in fact have gravitational attraction.
And to complicate it even further, once you delve into quantum mechanics there are virtual photons which have a non-zero mass...and so on and so forth.
Basically...you're trying to borrow little bits of a very,
very complicated concept, which is why you're going to run into problems.
you obviously don't understand that photons act in double, as a wave, and at times as a particle. But they are infact massless.
"The photon is currently understood to be strictly massless... If the photon is not a strictly massless particle, it would not move at the exact speed of light in vacuum, c. Its speed would be lower and depend on its frequency. Relativity would be unaffected by this; the so-called speed of light, c, would then not be the actual speed at which light moves, but a constant of nature which is the maximum speed that any object could theoretically attain in space-time.[21] Thus, it would still be the speed of space-time ripples (gravitational waves and gravitons), but it would not be the speed of photons."
from measly little wikipedia
"Why do photons produce pressure even though they are massless?
Because photons carry energy by virtue of their frequency""
from a stanford website
Gravity Probe B - Special & General Relativity Questions and Answers