Я хорошо, meaning 'I am well, (good)' in English, хорошо is an adverb describing 'am.' So when a person is asking "How are things?" and someone replies "Good." it is the same concept in both languages.
Similarly, it is possible to hear:
"Добрый день."
"Добрый день."
"Как ты поживаешь?"
"Спасибо, (поживаю) хорошо. А ты?"
"Тоже хорошо."
"Good day."
"Good day."
"How are you (getting along)?"
"Well, thank you. And you?"
"I am also well."