no, flood control does not mean the opposite.
storm water control involves "retention ponds", places that store the water and release it at a slower rate than it would flow if it was uncontrolled.
reservoirs also frequently serve as giant retention ponds, slowing down the flow from rain events.
but just like any other retention pond they have a maximum mitigation ability.
and this particular rain event pushed the dam beyond its abilities.
hence the attempts to release water.
the problem came from the unexpected erosion of hte spillway, which halted the water release.
the dam then continued to fill, and began to flow over the spillway anyway, further eating into it.
for an earthen dam overtopping or erosion are --BAD-- things (overtopping leads to erosion of the dam face itself).
this particular rain even would have still led to flooding of the local area.
the "worse flooding", ie, the problem being faced now, is only if the dam itself fails due to the erosion. its a possible outcome, but not something that has occurred yet. nor is it a certianty