It's only testing whether $q->param('intrests') (sic) doesn't match a vertical bar. For all the other values, it's testing whether they're false (empty string or zero).

This is a pretty awful way to structure an ifbut to get the effect you want you'd have to do:

if ($q->param('name') =~ /\|/
 || $q->param('site') =~ /\|/
 || $q->param('siteid') =~ /\|/
# and so on....
) {
# whatever...
[download]

It'd be much nicer to do:

foreach my $p (qw(name site siteid ...)) 
{
    if ($q->param($p) =~ /\|/)
    {
        error("$p has a vertical bar, that's bad");
        # or something
    }
}
[download]

HTH