According to Expreview, AMD conducted DKERN + RSA test for integer and floating point units, to arrive at a performance index of 4.53, compared to 3.5 of first-generation Zen, which is a 29.4 percent IPC uplift (loosely interchangeable with single-core performance).
The data in the footnote represented the performance improvement in a microbenchmark for a specific financial services workload which benefits from both integer and floating point performance improvements and is not intended to quantify the IPC increase a user should expect to see across a wide range of applications.
I don't see any evidence that they were running identical systems here. As far as we know part of the performance increase could be due to the improved manufacturing process increasing clocks. Furthermore, AMD themselves is trying to reduce expectations. Zen+ already had a decent increase due to better cache and clockspeed, wouldn't be surprised if AMD built off that along with an optimized pipeline could get you to the 29% increase in specific scenarios.

Call me skeptical, but I want to see a trusted report before I believe it. AMD always brags when they have something real - let them do a public demonstration and I'll buy in.