What can you infer from the sentence?

My roommate got home at 4 a. m.

The roommate is a light sleeper.

Something kept the roommate out late.

The roommate enjoys reading.

The roommate is new to the area,

Something kept the roommate out late.

Something kept the roommate out until 4 a. m.

What you can infer from the sentence is that something kept the roommate out late.

Explanation:

Using just the provided sentence as reference we can infer that the roommate was not at home since in the original sentence it says "got home", the original sentences does not give any further information about the roommate that could generate more inferences, we do not know if the roommate is new to the area, if they enjoy reading or if they sleep well at night.