Hi Niels,
Well, you cannot check that via WordPress core functions, as all of those items there are “mimiced” as post types, since the results page is built for that.
There might be a way though, via using the get_asp_result_field() function in there. Try:
if ( get_asp_result_field('content_type') == 'term' ) {
The “content_type” field should contain the result type – in this case you are looking for “term”, that represents taxonomy terms (taxonomy archive links).