Firstly disclaimer. This calculation is assuming your expected returns of 15% CAGR. If it is lesser, the savings will also be lesser.
But if markets return 15%, yes 28lks is what you would save on just a Rs 5000 SIP by investing into direct mutual funds.
Regular mutual fund has expense ratio of almost 1.5% higher for regular fund in this case. This means everyday 1.5%/250 extra is debited as expenses to a regular fund as compared to a direct fund (250 trading days in a year). If 1.5%/250 is removed extra everyday, the eventual impact is going to be extremely high as shown in the calculator.