What happens when you put 10V from a lab power supply on a single 3.2V LFP cell? The supply can not sustain the 10V (this would require an infinite current) and drops to battery voltage while outputting the maximum current it can provide. This is essentially constant current mode.
Not shown: once the battery would start to charge and increase its voltage, it will continue to do so until it reaches the power supply voltage (very bad idea), but would at that stage technically enter constant voltage mode while the current tapers off (at 10V, you would destroy your cell).
This is why it’s important to make sure you set the voltage on your power supply first before connecting it to the cell when e.g. top balancing. Additionally, this also shows that having a higher voltage temporarily connected to a cell is not an issue: the cell never sees this voltage.