Sounds stupid but perhaps they were hoping local sharks learnt biting boards wasn't rewarded by a meal & hence made it safer for surfers ?
You'd think, but I'm pretty sure they just found a reliable way to attract sharks that didn't involve breaking anti-chumming laws.
Thankfully there's not much reason to go to much trouble to train sharks against eating people, around here at least, since there really aren't very many attacks, especially when you take into account their numbers and the number of people in the water. But still, using a surfboard to attract sharks really strikes me as stupid.