Here is the source doc on the PMT events:
<i>The measured data from these tests shows DD fusion neutron production (Fig. 7) of about
5E4 neutrons over a period of about 0.2 msec (less than the data rate interval), which also shows the
emitter current of injected electrons (Fig.
to run at about 4-40 A during this short pulse period of
fusion generation. .This peak pulse period is also indicated by light output measurements from the
photomultiplier tube detectors (Fig. 9). The PMT showed a rise to peak output as the internal
machine neutral gas was fully ionized, a flat-top during the onset of the external glow discharge, and
a rapid falloff as this condition was passed. The actual rise was certainly faster than the data rate
showed, so that at the peak, the edge electron density was a maximum, the full well depth was
established, and DD fusion was taking place. Beyond this time, the potential on the machine dropped
(Fig. 10) as external arcing (from the tank walls and feedthroughs) took over, the external current
rose to very high values (Fig. 11), and the system discharged and shut down.</i>
So presumably they understand the difference between light from glowing plasma and light from something that is not glowing plasma.
<i>Fourth, the PMT registered a large pulse for 4 of the 5 tests, indicating a large light output, in
the center of the machine, at exactly the time of the counts. There is nothing there in the PMT’s
field of view to cause an arc (which usually is the culprit for noise).</i>
It proves little or nothing by itself, of course, but if I'm reading this right it sounds like it could be supporting evidence.