This isn't entirely clear

I'm not quite sure what you mean by the "rule on thousands". Can you provide an example?

I think the lessons on Kwiziq with pairs of sentences all show the French first in italics and the English underneath in slightly bolder text and this one is no exception. It’s a bit confusing that the title is  "Learn how to write decimal numbers in French" whereas the lesson includes thousands with no decimal point but I guess it’s to underline the fact that where English has a decimal point, French uses a comma and where we use a comma to separate the thousands, French has a space or more rarely, a point/full stop (see the 4th section).