The Sage Advice Compendium has this text:
If you cast a spell, such as healing word, with a bonus action, you can cast another spell with your action, but that other spell must be a cantrip. Keep in mind that this particular limit is specific to spells that use a bonus action. For instance, if you cast a second spell using Action Surge, you aren’t limited to casting a cantrip with it.
From this tweet by rules designer Jeremy Crawford, I understand that if you cast a spell using a bonus action, then cast a cantrip as an action, and then use Action Surge, you can only cast another cantrip with that additional action. However, I don't understand the example they wrote. It seems to be misplaced.
Can anyone elaborate on what is the meaning of their example? Do they mean "If you cast a spell as a normal action (not as a bonus action), and then Action Surge, you can cast another spell on your second action."?