💡 Where your data comes from does not matter. The getCellContent callback is a data fetcher. This is a fundamental difference from other libraries that expect you to pass data in a format they expect.
allowOverlay has been set to true. This allows the overlay to come up. For explanatory purposes the readonly field is being set to false. This is the default value, setting it to true would allow the overlay to come up but not allow editing.
Implementing the onCellEdited callback allows responding to cell edit events. Edit events pass back a mutated version of the original GridCell returned from getContent.