Hi,
True for continously switching switchers. But with that low load burst mode operation or pulse skipping mode is possible.
Then - I imagine (I really don´t know it for sure) - it could be temporarily (during switching) above 250mA.
For thermal considerations - i agree - that one will calculate less than 100mA ripple.
In either case: I recommend to use a capacitor that´s ESR is specified for high switching frequencies.
The first one is called "Low impedance, Downsized, 105℃" with ESR and ripple current specified at 100kHz.
The second is called "Standard, 105℃" wich is specified at 120Hz. --> I assume it´s use is for mains frequency.
Klaus