Yep, you're quite right. And it is a sample - a subset of less than a thousand, iirc - that they use for Oztam ratings.
Plus we're likely more interested in viewers on all platforms than those ratings per se.
I believe their
Video Player Measurent works differently. What they've said:
OzTAM’s VPM Report is a world-leading approach to capturing census level data on exactly what content is being played on connected devices.
… broadcasters currently include ABC, Seven Network, Nine Network, Network Ten, SBS and Foxtel.
So, they take some fine-grained data on streams. A Top 5 round-number summary of which WCR has linked and it does list Brumbies v Chiefs having around six thousand being connected across the duration of the game.
Click pic to embiggen
That link obviously doesn't have Kayo breakdown figures, though. Where are they available, assuming they are available?
Nor anything on My Football Live.