The discussion was around mobile IP connections. I am not sure if your calculation includes for example (just guessing!) other mobile carrier branded services using their network (MNVO[0]), non consumer (eg. IOT type or vehicular) mobile nodes, etc. I would trust this person implicitly as I used to work for them, they are an engineer not a salesperson and they are not known to extend the truth. While no information is infallible and perhaps they were wrong, given their position, however, I doubt it.

[0] https://en.wikipedia.org/wiki/List_of_Australian_mobile_virt...

Edit: Seems my info was bad. Disappointing! Latest stats page 9 @ http://clients3.weblink.com.au/pdf/HTA/02127798.pdf and page 31 @ https://www.acma.gov.au/-/media/Research-and-Analysis/Report... They are indeed third (last!), though currently the fastest growing. Their MNVO base = 350K customers, total = just under 6M customers. Guess it shows how long I've been outta dodge :)