Yes, if you check the fare components in the fares for both 20671 and 20672, there is hardly any difference in any other part, apart from the catering charges. Catering charge for 20671 is Rs. 364 (CC) and Rs 419 (EC), whereas for 20672 is Rs. 530 (CC) and Rs 613 (EC). Looks like, lunch will be skipped for 20671, and that's why the morning catering (probably includes morning tea and breakfast) price is less.