Good question, it's my understanding that if you gradually press the break pedal regen is tried first, if regen maxes out and you keep pressing harder, the friction breaks will kick in. So in your case, if you only pushed on the break pedal hard enough for the 4 dots of regen to come on and no harder, it should be just regen.
Because of this and I'm not always sure if I'm pressing too hard on the pedal, I like to use B(or ECO on my '13S) and only use the break pedal if regen isn't enough to slow the car down.
Our Prius is the same, pushing the pedal lightly first kicks in regen, then a harder push will begin to apply the friction breaks. Personally on our Prius I don't use B mode as I feel it stops the car too much and doesn't allow coasting, I just lightly feather the break pedal if I only need to stop slowly(or sometimes I engage the B mode to stop or for long hills). IMO my Leaf has is just about perfect regen in ECO(no B mode on S model Leafs, at least mine) with just enough regen to slow the car but not too much as to impede coasting. Probably my favorite would be steering wheel paddles like on the Bolt, maybe some day.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a