So, the odd thing here is that we don't call eventHandler() for button presses. Instead, you use
playdate->system->getButtonState(PDButtons* current, PDButtons* pushed, PDButtons* released);
to return the current state of the buttons, which buttons were pushed in the last frame, and/or which buttons were released in the last frame. Any of the arguments can be NULL. I was going to replace that with calls to eventHandler() but all of the game devs that were using the C API said they preferred this polling function. Obviously this is a point of confusion, so I'll add kEventButtonPressed after all (and leave getButtonState()).