I see three problems right off:

First, the snippet of the file that you show is space-delimited, but you are splitting each line on the tabs.

Second, when counting elements in an array in Perl, you should start at zero, not one. HIGH/LRR/LOW is in the 7th column which would be element number 6 (or $t[6]) if the line is properly split.

Third, I don't think you mean to test that column 7 matches ALL of the keywords at once.