Minimum output current of DC-DC
The typical reason for a minimum load is that the leakage inductance in the magnetics causes the output voltage to be significantly higher than the nominal output voltage when lightly loaded.

That could exceed the maximum input voltage of your LDO or (conceivably, but not likely) some maximum inside the DC-DC converter. I think the latter is quite unlikely, and they even specify the no-load input current, so if you have plenty of margin on the LDO, I think you’ll be okay.