"Did you make the food?"
Translation:An ndearna tú an bia?
No, it's not because déan is irregular. You can tell that déan is an irregular verb because the negative past tense form isn't níor dhéan, but ith is an irregulat verb, and it's past tense negative form is still níor ith mé, as it would be if ith was a regular verb.
Irregular verbs are irregular. But they aren't all irregular in the same way - in the case of ith, the present and past tense forms are "regular", and in the case of tabhair the present and past tense follow the same pattern (tugann and thug) and in the case of clois the negative past tense form is just níor before the past tense form, just as it is for regular verbs, etc. You can't predict what all forms of the irregular verb are going to be from the root - they wouldn't be irregular if you could!