I ran your code through Deparse, and this is what I got:

$ perl -MO=Deparse,-p
print $lines > 1 ? 'plural' : 'singular';
print ($lines > 1) ? 'plural' : 'singular';
__END__
print((($lines > 1) ? 'plural' : 'singular'));
(print(($lines > 1)) ? '???' : '???');
- syntax OK
[download]

While in the first line all that follows print is print's argument, in the second line only $lines > 1 is the argument

So, besides the precedence rules cited by jsprat and stephen, you should remember another rule I found somewhere in the Camel Book:

if it looks like a function, it is a function

that is: if you enclose something in parentheses just after a function, e.g. print, what's enclosed in parentheses is considered that function's argument

Ciao!
--bronto

# Another Perl edition of a song:
# The End, by The Beatles
END {
  $you->take($love) eq $you->make($love) ;
}