Scams like these

[Forg]

Does the random aspect apply to the country code as well, or is that part mostly reliable?

While I'm not expert on the topic of configuration of auto-dialling systems, from observation I'd say that they need to set it somehow. Seems pretty common that if you get the same SPAM call in a day, it "comes" from the same country.
In fact it's normally regional too, come to think of it, if the first one "comes from" Queensland the 2nd and 3rd one on the same day are normally "from" Queensland too. But that may be the result of cycling through all possible numbers, too.

 

[There'sOnlyOneJimmy]

So, the country/region code is configurable by the bad guys regardless of their actual location.