I would have expected the Flow Control software to tell you the truth about the fans connected to its pump unit. On the other hand, third-party software sometimes needs to be calibrated to be able to give you the right readings. MORE importantly, such software normally gets ALL of its info to show you from the mobo headers. BUT in that AIO system, the rad fans are NOT reporting any speeds to the mobo, so that software can NOT tell you the rad fan speeds. It CAN tell you the speed of SOME things, but it simply makes assumptions about WHAT item is plugged into which mobo header. So the labels it tells you for the speeds it displays can be quite wrong!
In Flow control next to the slider for and and pump speed settings is an icon you click on to set up the fan "curve". That is a graph of what speed the fan should run versus what temperature the CPU is at. Now first of all, most such system have a few choices for how this is done. They typically include a "Normal" automatic control system with pre-programmed settings that wiill make constant adjustments of rad fan speeds (and maybe pump speeds, if you let it) based on the actual temperature measured by a sensor inside the CPU chip. Often you also have choices to set a fixed pump speed either full speed or some reduced "quiet" speed. And often you have also a choice to set your own "fan curve" instead of the pre-programmed one. So check how that is set.
Now, in choosing how this is done and what fan speeds you like, remember that the fan SHOULD speed up and slow down as your workload changes and heat generation changes. Although fan NOISE relates to fan speed, the resulting COOLING also is governed by fan speed. Your first priority must be to ensure your CPU DOES get enough cooling at all times.