This has been discussed and answered below. It is the purpose of the lesson to indicate the difference in the general use of the mathematical separators between French and English systems. Cécile and Laura have answered this specific example, and there are more explanations below. 

If you think the quiz is wrongly written/marked you can submit through the report issue button for verification and correction if required. 

The number written 78,005 in French is written 78.005 in English - it is 78 decimal 005

The number written 78,005 in English is written 78 005 in French. It is 78 thousand and 5.

As you can see in the attached link, it is not just French versus English, and it is also a bit more complicated (as the lesson also addresses).   

https://www.languageediting.com/format-numbers-eu-vs-us/

Yes !!  kwiziq are causing confusion by not distinguishing between numbers, sums of currency and decimals.  They are calling everything numbers.

I am English living in France.

I agree with all the above - Deleted, Andrew, and Jean. I have stopped answering this group of questions because I so rarely agree with the given answer. The questions are not clearly written to say whether or not it is relating to currency. In UK we do not use decimal points to denote thousands. Marjory

Hello again Deleted.  Yes I agree again with what you say. These answers are not correct. 

I think the problem arises because American English is being used and American English is not the same as British English especially where these numbers are concerned hence the confusion. Full stops are not used to denote thousands in British English. Commas are used. 

Marjory