No, it's a misnomer. Technically "obasan" does mean "aunt", but it can be used for any woman in/past her mid-20s by someone younger.
You'll find the same thing with words like "oniisan" and "oneesan" ("older brother" and "older sister", respectively, but usable for a young adult by a younger person).
...it feels incredibly good!Aunt's... deepest place...au-I'm going to cum loads in there!Aunt's pussy is the best!
"obasan"/"Aunt" is a term used in Japan that doesn't necessarily mean that the object person is actually related to the speaker.