It's because those are two different tenses. While "he eats bread" Is present, "he is eating bread" is Present progressive. Since there will be two different tenses, there will most likely be two different conjugations, or set ups of sentences. They are not the same. Hope that helps!
'He eats' and 'He is eating' are virtually identical in English. If there is a big distinction in Irish that can only be captured by assigning the English differently then that should be emphasized in the notes. Otherwise either should be accepted. 'is eating' is much more natural in English.