It might have been none of the above. I assume yours is a classic chain break where one plate fell off a pin and the other is bent open breaking the chain.

Nothing you did with regard to your chain care caused this, it most likely is from one of two common causes.

1- bad closure at the factory. This might be one of the most common reasons for chain breakage. The people on the assembly line close hundreds of chains daily, and sometimes fail to make sure that the pin is through both links and centered properly. If you sill have the damaged link, the giveaway is a bulge on the inside of the outer plate that came off the pin (not the bent one still attached). That shows that the end of the pin being pushed through wasn't lined up and bent the plate before find and going through the hole.

2- bad shifting. Hard shifting under load with a modern index system is incredibly destructive to chains. They can withstand hundreds of pounds of tension, but when twisted while half engaged on two sprockets is very stressful. When you shift under load the chain is forced tighter into the twist and the link's are pried apart eventually coming to the end of the pin. The chain is now weakened but can continue to work for days or weeks until a high load is put on it on a steep hill, then snap. It's the same way a rope that's been frayed won't break until stressed to the max.

The second is a common cause of chain breakage among new riders, who tend to shift too late, and are forced to try to shift under load. Try to anticipate your shifting and shift while you still have enough forward momentum to lighten the pedal pressure through the shift.