Power LED without driver
I think what you are seeing is that because your 30V power supply is close to the 25V typical Vf for your module, your LED module is driven to a point on its Vf vs Current curve where it doesn't burn itself out.
Below is a typical LED Vf curve from a good article from Meanwell about LED drive voltage.

You can see that as the current increases, the drop across the LED increases.  If your 30V does not put the operating point above the maximum current, then your LED runs just fine.
One problem is that Vf varies on a part-to-part basis.  Parts from a different batch could run at much different brightness or even burn out at 30V.
Another problem is that as shown below, Vf goes down with temperature.  So as your LED warms up, with a fixed voltage drive the operating point will move to higher current where the Vf is again 30V.  This will cause it to heat up more, reducing Vf more, and potentially burning out the module.  This is called thermal runaway.