So one of two things appears to be happening.
Either you actually ran the code using single quotes instead of the double quotes .
outfile='&outpath/shorts.csv'
The macro processor ignores string literals bounded by single quotes.
Or the macro variable OUTPATH was not defined. In that case you should have received a WARNING message:
7729 %put "&outpath/myfile.csv";
WARNING: Apparent symbolic reference OUTPATH not resolved.
"&outpath/myfile.csv"
Either way once the operating system sees that SAS is using a RELATIVE pathname so it tries the create a file under the current working directory, which appears to be on that disk/sharename that is mounted as the D drive.