Can a power supply have too much amps?
You are correct. The load normally dictates the current. I say normally, since a fault condition can take whatever you are plugged into can supply. 

Cost and size usually dictate what kind of power supply we want to use for a particular application. You want it big enough to have enough margin for tolerances, but not so large that you are paying extra or requiring a larger enclosure.

Sometimes, for simpler circuits, we can calculate the required currents. However it is also common for larger boards to build and test circuits with larger supplies, eg, bench supplies so we know exactly the kind of currents we need. Then design, or chose, the appropriate power supply to drive it. I think that is what your quote is alluding to. That is..The Raspberry Pi Zero board will draw a maximum of 2.5 A.

Another factor you need to consider is that regulator circuits, especially switchers, do not have a flat efficiency curve. Too large a supply can run at horrendous efficiency numbers with a lot of ripple.