An is the question word here. Gaelic has two verbs that equate to the English to be. bi in the present tense is the one we know with tha, chan eil, a bheil?, nach eil?, and is used when describing things - my cat is hungry, my cat is not hungry, is my cat hungry? isn't my cat hungry?. I.e. the forms of bi are usually used with adjectives.
is is the other "to be" verb - the present-tense forms are is, cha/ chan, an/ am?, nach?. is is used to identify things, and is usually used to link two nouns (linguists sometimes call it the "copula" for that reason, others the "assertive" verb) - my cat is a pet, my cat is not a pet, is my cat a pet? isn't my cat a pet? It is also used in various set expressions that are not quite so easily explainable - "is toil le x" is one of these, which you just need to learn. The forms with "me/I" are is toil leam, cha toil leam, an toil leam?, nach toil leam? - I like, I don't like, do I like?, don't I like?