Unknown subject considered to be feminine -- how?

Question

This sentence was considered correct:  
Tu es apparue comme un ange.
But that doesn't that assume we know that the subject is female?  If we don't know, why isn't it Tu es apparu comme un ange.

Accepted Answer

Rebecca,
this is an example translation from English to French employing the 2nd person singular informal  - that is you personally are addressing someone directly, a single person.
Depending on whom you ‘see yourself’ talking to, male or female grammatical forms can be correct and rightly should be accepted if it is a ‘free translation’, unless instructed otherwise.
In a drop down list that indicates all correct answers to be marked, if both ‘es apparu’ and ‘es apparue’ are given, both will need to be selected as potentially correct answers. 
As applied to ‘personal’ pronouns, the masculine is used for known male subjects, or groups known to be all male or possibly or definitely of mixed gender. 
Where we might say ‘someone’ in English for an unknown 3rd person - eg "someone appeared like an angel", quelqu’un’ fits in French, and masculine grammar applies with the indefinite pronoun.
 https://progress.lawlessfrench.com/revision/grammar/how-to-say-someone-or-someone-else-quelquun-quelquun-dautre-indefinite-pronouns

Answer

Bonjour Rebecca,
Maarten is correct as to the agreement of "apparu.e" and as to the way the dropdown menu works if two answers are correct.
Also to supplement Maarten's answer, "un ange" is always masculine eventhough it can be used for a woman too. After discussing this point with my other colleagues, we made the decision to remove this test question as we can see the ambiguity related to "un ange".
I hope this is helpful.
Bonne journée !