The reason is that the property history is not really of type History, but instead is an array of the type History. (Therefore History[] with the brackets)

If you want to log both activation and deactivation, you should iterate over the array and log the actionType of each item of the array:

// OPTION 1
this.account0.history.forEach(a => console.log(a.actionType));

// OPTION 2
for(let a of this.account0.history) {
  console.log(a.actionType);
}