Figure 1 in the paper shows that six and eight year olds are a lot worse than adults, while 10 year olds are only somewhat close to adults. In this figure they asked the participants to classify if a bark was barked in three different context (stranger, alone, play). All age groups were able to tell when a dog is barking at a stranger, that seems to be pretty hardwired into our brains. The rest seems to be experience.
In figure 2 they asked the same age groups to associate different emotions to the barks in the three contexts. Similar classification findings as in the figure before. The authors discuss though that associating human emotions with the dog's real "inner state" is difficult and maybe not possible.
So the content of the linked article is very misleading and suggest that the journalist didn't really care to take a look at the paper. But the paper itself is interesting.
It would also be fun idea for a novelty app that can tell you how your dog feels. MVP might be to turn the data from table 1 of the paper into a very simple classifier. The data is however only based on 8 dogs from the same race.