Translation:It must have followed me because it is hungry.
The proper translation in English should be: "It must have followed me because it WAS hungry." (agreement of tenses). Everything is happening in the past, so we cannot use the present form of verbs (is, are, goes...), but past forms such as 'was', 'were', 'worked' 'went' etc.
I must have missed this one the first time around, but either tense could be appropriate in this case.
If we were talking about a dog, it would be perfectly normal to (at the present moment) look at the creature and say, "It must have followed me because it is hungry." If we were recounting the incident after the fact, then we'd use the past tense in the dependent clause. But the main clause alone does not indicate past or present. With the "must have" meaning, it's more of an indication of mood than time. . Since the Italian sentence uses the present tense, we can assume the former context is intended here.
I only meant that either tense would be grammatically appropriate in English, not that either tense would be an appropriate translation. As mentioned, the Italian sentence very clearly uses the present tense, so it should take the same meaning. If the Italians sentence had said "...perche aveva fame," then the past tense would make sense in the English translation.
Instead of 'it had followed me', you could translate 'it will have followed me ...' and that would be correct. However, a translation that uses 'must' is also correct. See the Lesson Notes that Duo provides for this unit, or see the other comments on this page, especially those by nerevarine1138.