by this time or by that time

[lagoo]

When Sinclair was 10 years old, his father moved the family from Baltimore to New York City. By this time, Sinclair had already begun to develop a keen intellect and was a voracious reader, consuming the works of Shakespeare and Percy Bysshe Shelley at every waking moment.
Link: https://www.biography.com/writer/upton-sinclair\

Is it an error using ‘this’ instead of ‘that’? If it is correct, what does ‘this’ refer to?

 

[GoesStation]

It's correct. It refers to the time when Sinclair had attained the age of ten.

 

[jutfrank]

I suggest you use that. Why do you prefer this?

 

[GoesStation]

The text's author wrote this, which I think increases the sense of immediacy.

 

[jutfrank]

I suggest you use that. Why do you prefer this?

The text's author wrote this

Right. I obviously wasn't paying attention when I asked that. Thanks.