The RPMs jumped because of the converter. It's loose enough that with the extra torque of boost, it stalled to 4800rpm at full boost. Then, it held 4800rpm as the rear tires are cetching up to the stall speed of the converter. If he kept in it, the rpms would start rising as you'd expect to see. I would imagine he didn't run it to redline because 130mph is generally frowned upon while on the street. It's familar to me because my 2.3/c4 is similar (except a lot less power). At full boost, I can generally blow the stock pinto converter to 4500 (stalls to about 2500 with no boost).
That video is what real power looks like boys. It may not seem amazing, but that kind of acceleration at highway speeds in 3rd (c4) takes some serious power and torque.
If I ran it to redline it would be over 150mph. The true stall is about 3000, but the boost makes it stall more.
The car just made 656rwhp through this C4 at 20psi.
It made 480rw with 12psi.