Probably you should first consider that our browsers contain a fully capable programming system which this golfed program abuses as an expression evaluator. :-) By comparison, this C program [1] (hints are at [2]) is a stripped down spreadsheet program for X, and it only has an RPN evaluator (probably to make a room for graphing features?).
Language detection works on language trigrams, and are trained on human language. I bet punctuation is stripped during preprocessing. So it's not surprising that code will have false positives.
[1] http://www.ioccc.org/2000/jarijyrki.c
[2] http://www.ioccc.org/2000/jarijyrki.hint