A man appeared on the corner the cat had been watching, appeared so suddenly and silently...

[diamondcutter]

A man appeared on the corner the cat had been watching, appeared so suddenly and silently you'd have thought he'd just popped out of the ground.
Source: Harry Potter and the Sorcerer's Stone, J. K. Rowling

Did the author omit “and he” before the second “appeared”?

 

[jutfrank]

The ellipted subject is the man—the subject from the previous clause.

 

[Ostap]

Is the usage of the comma really idiomatic in the OP? Any of the options below sounds better to me. "Appeared" starts a different thought and it feels a comma is not enough.

A man appeared on the corner the cat had been watching. Appeared so suddenly and silently you'd have thought he'd just popped out of the ground.

A man appeared on the corner the cat had been watching — appeared so suddenly and silently you'd have thought he'd just popped out of the ground.

A man appeared on the corner the cat had been watching; appeared so suddenly and silently you'd have thought he'd just popped out of the ground.