He is correct but it is not evidence that it formed in a lower gravity environment. It is consistent with being from the Moon where there is essentially no oxygen and very little water (in most places).
IANAG (I Am Not A Geologist) but I do understand the basic physics so I think it must be about the effect gravity has on whether the flight time of molten ejecta from an impact is long enough to solidify before hitting the ground.
A primary impact involves an object not already part of the moon; it always hits at (or usually well above) escape velocity. A secondary impact is ejecta from another impact that returns to the surface; it always hits at less than escape velocity. Determine the impact direction and energy of a secondary impactor and you can estimate its impact velocity and therefore its time of flight in the known low lunar gravity. The models simply wouldn't work so well for so many samples unless you assume lunar gravity, so that's the evidence they were formed in a low gravity environment.
That is one explanation. Although many of the glass beads (some of the green and all of orange AFAIR) are linked to fire fountains rather than impacts.
Impacts do generate small glass beads on earth, we call them microtektites, or impact spherules in older rocks. These are almost always spherical, sometimes dumbells or other shapes, and have had experienced substantial flight times. The Australalite microtekite field extends to Antarctica from an as-yet undiscovered impact in SE Asia.
For fire fountains the longer the time they are in flight the more likely the glass droplets will form spherical shapes. Obviously at lower gravity (e.g. the Moon) they will be thrown higher and fall slower than given the same impetus on Earth.
However the height of the fire fountain is driven by the rate of degassing (again AFAIR) and the amount of dissolved gas, which is highly variable on Earth and (I assume) the Moon. This will also vary according to the gas, on Earth it is H2O and CO2, on the Moon mostly CO. So we can't assume that lunar beads will have spent more time in flight.
Cooling rates are also important. All glass beads cool quickly, as indicated by the fact they are glass. However Lunar lavas probably at higher temperatures than terrestrial ones, so would cool slower, I suspect. They are also in vacuum or at least low pressure, so will cool differently to beads.
The more viscous the lava the slower it would assume a spherical shape, so as most terrestrial lavas are more SiO2 rich (and thus more viscous) than lunar ones, they are more likely to be frozen into less regular shapes.
So there are many factors, gravity being just one of them.
