'talk about ...' is usually used in conversation to emphasise what follows, 'heathen' in your example. This has probably not been mentioned before.
'talking of/ about ...' is used in conversation when you want to say more on a subject which is being discussed, or move on to a related subject.
A. You've met Henry. What did you think of him?
B. Henry? Talk about boring! He makes watching grass grow seem fascinating.
A: Talking about grass growing, I was mowing our lawn yesterday, when ....'
Student or Learner