Your assumption is not really related to P1 comp upgrades.
While this particular situation may have been an op up, it's unlikely imo.
While Matt didn't specify how far ahead of flight time he checked in (ie: 24h or 2h) there are usual giveaways as to a P1 upgrade. One, a message from the VIP Team on the BP itself(though this does not always happen) and two, these upgrades usually show up around 24h before. They tend to not be last minute. Indeed last minute upgrades are almost certainly op ups (which are rare, but not unknown with QF) and that would occur due to a flight being oversold or possibly an a/c sub.
At one point I would pick flights with A330's on Saturdays or midweak lunchtimes etc which were pretty empty in paid J and took a gamble. Sometimes it would work out (and watching the flight in the days prior would show this). These were always situations where it didn't matter if it did or didn't happen and I picked flights convenient to me not just to score a "free' upgrade, but when opportunity would arise I gave it a go.
The metrics are opaque and may have changed since the pandemic. the comp upgrades do still exist, but seem much harder to get (which likely is also a side effect of reduced capacity/increased demand). Because P1 upgrades have usually (in my experience anyway) been processed a day or so prior to travel, any points upgrades and so on have usually been processed already for CL/P1/WP.
Anyway it's a nice thing to get of course but certainly nothing to rely on.
