That's not the raw data, it's adjusted to match groups for a comparison. If you look elsewhere in the paper:

The overall success rate on first time ventures is 25.3%. Not surprisingly, serial entrepreneurs have an above-average success rate of 36.9% on their first ventures: venture capitalists are more likely to be more enthusiastic about financing a successful entrepreneur than one who has previously failed.

That's for IPOs only, adding in companies that were acquired, and companies that remained private but made their owners a good amount of money via compensation packages and future sale or IPO would further boost the stats. See my 80,000 hours posts on this.