I tried in Indesign CC 2014. It shows the correct value. What version did you checked?
Also try like this:
I tried in CC2014 and CS5.5. There are both problems.
alert(app.activeDocument.textFrames.item(0).strokeWeight) is also same value.
Is it correct you were the D&D or place file?
I placed and drag and dropped the file, both are giving correct results
Hum... Thanks for comment.
Somebody please check only one more.
I want to make sure that is my only problem occur.
No problem over here on CC2015