Well I agreed with you somewhat until your last sentence. DUO accepts bug reports or suggestions anytime. You are making the point that this word ('"retires") in "english" is a homonym. A word that is spelled and pronounced the same that have different definitions. This is a French lesson on the phrase, expression, "he is retiring - he retires"/ "il prend sa retraite". You suggested "he is retired" is the subject.
"He is retiring" would be more idiomatic in English. That action is considered a process, typically involving deliberation. Another example where the present progressive would be more likely: "He is getting married" instead of "he marries." "He retires" suggests that that activity is part of his regular, everyday activity, as in "Jesus saves." "He retires at nine o'clock" would mean "He goes to bed regularly at nine o'clock." "He marries" might be used in "He marries his parishioners," meaning "with each other."