"He had the cold."
Translation:Bha an cnatan air.
It is not normal in any major dialect to say the cold, as shown here. It is so rare in the present tense that it generates an error - i.e. it was not found at all in the British English sample. This contrasts with the flu which is much more common than flu.
I think this is because there are perceived to be lots of them, so the definite article makes no more sense than the broken finger. You can have the flu twice but you have two colds or two broken fingers.
There may well be an exception where the English is heavily influence by Gaelic, but I do not think this course usually defaults to 'Gaelic English'.
The cold is a really common way of saying it in the west of Scotland, especially in the present tense: "I've got the cold!". You might hear "I had a cold last month" If it doesn't show up in a particular search of books that doesn't mean it isn't used. Try this: https://scotssyntaxatlas.ac.uk/linguists-atlas/?j=y#6.75/56.304/-5.347/Q46/And/all/1/12345/both/null/point The site has a lot of interesting stuff. I think you might like it.
A very interesting link, thank you. It shows some feature are much more common than I thought and some much less.
Sadly, I think the problem is that this is an atlas of Scots. Most people who manage to get into the Google corpus either choose to write in English, or have their work mutilated by an editor so it looks English. I (and the survey) think nae and wisnae are pretty common in Scots but they are not so common in English according to Ngram
aig is mostly used for things – material objects you can own, while air is used for feelings, states of your body, and some body parts (eg. tha an t-acras orm I am hungry, I have the hunger, tha falt purpaidh air he has purple hair, bha an fhearg oirre she was angry, she had the anger, bha an cnatan air he had the cold).
I'm not sure of the point you are making. It is indeed an illness, but it is an illness called a cold in English, not the one called the flu (which is not used with the indefinite article anyway).
A cold and the flu are different diseases, caused by different viruses. I have never heard cnatan used to mean 'the flu'. Have you? Nor has AFB or Dwelly. Mark gives cnatan mòr for 'the flu', but I have not heard that. Even if it is used, Mark is clearly drawing a distinction between cnatan and cnatan mòr.