They use constant voltage driver that takes full driver current and divides between all the boards. So instead of running at roughly 2.1 amps per board on constant current driver, they run roughly 2.5 amps per board.
Parallel module wiring is considered less safe due to greater risk of thermal runaway situation. If you have a module fail or wiring issue that causes a module to go out, the whole driver current would be available to remaining modules. In this case, board current could go from 2.5 amps to roughly 3.3 amps. Which is roughly 20% more current than the boards are rated for.