At first I thought, "yeah, it's possible his "half an hour" quote is an easy mistake anyone makes" because I know a lot of people who will say, "So i went to the shops/was asleep/dropped into work for maybe half an hour" and they don't realize it was more like 2 hours than half an hour. People tend to inaccurately recall time when they reflect on what they've been doing and how long they took.
However - yes, Mt Cootha is a WEIRD destination to choose. It's basically Brisbane's Make-Out Point! You can see all the cars lined up on the side of the road overlooking the view of the city, and you can gather what people are doing in these cars. Let's just say they're not having a conversation, usually (though I guess you could use it for talking only). And, ahem, this behaviour is not only restricted to inside cars... I saw a couple having intercourse on a picnic blanket on the grass RIGHT below the rotunda area (underneath the telescope) once, at dusk. I burst out laughing in shock and amusement and they gave me a dirty look. Um, I'm not the one doing this in public!
It does seem weird that they chose Make-Out Point to have this conversation. Surrounded by lovey-dovey couples and tourists.