Another consideration the designers of the controller were looking at is having all of those 12 lights come on at the same time, inrush current is what they're thinking of there. If you hit that threshold where the inrush current overcomes your supply breaker, it will trip (even though the connected load is under the rating of the supply breaker). At that point you'll simply have to adjust what you're feeding via that 50 amp supply & controller. Same thing as an A/C only drawing say 20 amps but needing to be supplied via a 30 or 40 amp breaker. Normal operating current doesn't change, it's just the inrush they're trying to account for. Most home distribution systems (home electrical panels) don't have breakers that have different trip curves but industrial panel set ups have breakers that can be sized closer to those constant loads via their trip curves, if you're following me.
The breaker will take care of itself, as it's very singular in design, in relation to the overall controller/ supply situation.