Exactly. They did nothing illegal or immoral.
BUMP: those downvoting. It's a serious question. The article doesn't explain the student's methods. I really don't know what they did to game the system. Is it well known?
When the jackpot reached a certain point, they'd increase the payout on the lower tier prizes (match 5, 4, 3) from ($4000, $150, $5) to something more significant.
Instead of needing to match all 6 numbers (range 1..46), you could get a good return by only trying to match a smaller set. I guess they worked out a good distribution of tickets to purchase that covered a large percentage of those possibilities. They were purchasing 300k tickets to guarantee their 15-20% ROI.
[0] http://en.wikipedia.org/wiki/Massachusetts_Lottery#Cash_Winf...
"The inspector general’s report claims that lottery officials actually bent rules to allow the group to buy hundreds of thousands of the $2 tickets, because doing so increased revenues and made the lottery even more successful."