Catalysis of the reaction: 1,6-dihydroxy-2-methylcyclohexa-2,4-dienecarboxylate + NAD+ = 3-methylcatechol + CO2 + NADH.
1,2-dihydroxy-6-methylcyclohexa-3,5-dienecarboxylate:NAD+ oxidoreductase (decarboxylating)