I think it has to do with monsoon TT. Next run of Goa Raj is scheduled on 10 June ex NZM the day on which Monsoon TT starts in KR. So as per Monsoon TT Goa Raj will arrive around 14:40 hrs. So Lunch will be provided onboard on Day 2. Hence the extra fare.
TVC Raj has 3 more services ex NZM in Non Monsoon TT. Let's wait till Next weekend . It will be clear.