While I am VERY new to learning dutch, it would seem that "the man is eating an apple" should be acceptable. What am I missing?
"Mens" translates to 'human/person' not specifically to 'man' as in a male, so translating it to "the man" would be incorrect here. You would be thinking of "Man" or it's plural "mannen" which translates to "man" or "men".
Neverless It does not translate to Human. The person perhaps. How can you say it translates to Human/person when both of those terms are never used by English speakers? It accepts 'The person is eating an apple' So you cannot be too critical, Remove the word human to give it more balance.
The purpose of the lesson is to teach you the dutch word for human whether or not the sentence is logical to you. If it helps, find a context where is does make sense ie imagine an alien observing a captive human eating an apple.
From what I can tell from the course so far, there isn't a difference, unlike in English. Both use the simple present "eet".