Why is the example: Oh I watched that too yesterday, but in the test became, I watched that yesterday too, thus failing the test?

Hello Ann... the confusion here is in the English!

Obviously not Australia...

Yes I watched that yesterday, too. is correct

Yes, I watched this one too yesterday.. the difference is subtle I agree but I think "this one" would need celui ci

.. you thought French was difficult!

The example is

I think that is more to do with the vagaries of the English language.. the French is just fine!

Agree with Mark. The 2 sentences in English could have different meanings, depending on context. However the testing point was the meaning of 'ça' and although it can mean 'this, that, it", it does not mean 'this one', so that answer had to be wrong, as was the one with 'aussi' translated as Australian. 

(We would always use a capital A for the famous abbreviation of our nationality, and almost invariably spell it "Aussie", aussi !)

What is the answer please.

The correct answer to the questions is always noted on the results page following the quiz. 

If you, mean what is the answer to the reason for a word change - perhaps unintentional or perhaps to extend a (little) bit beyond the lesson. There is rarely only one way to translate a sentence from one language to another. 

Oui j'ai regardé ça aussi hier mais dans le