Same source says that it definitely came to Europe from China though, a few paragraphs lower:

These findings do not at all suggest that the virus originated in Italy, but they endorse the idea that the virus was likely spreading in China before the first known cases and that could have been circulated by travelers given direct the connections between China and European and US countries, particularly the Northern West and East Italian regions, which are among the most industrialized and connected areas of Italy. Evidence used to support this hypothesis comes from a comparative genomic analysis of more than 175,000 genomes, which delineated 22 distinct SARS-CoV-2 haplogroups with a broad geographic distribution within China, pointing towards an early emergence and widespread cryptic circulation of the virus well before its isolation in January 2020 [25]. Recently, Kumar et al. reconstructed the mutational history of SARS-CoV-2 using a so called ‘mutation order approach’ (MOA) [26]. From their analysis of more than 174,000 genomes, major mutational fingerprints revealed that it is useful to identify and track the spatiotemporal evolution of novel coronavirus. The progenitor genome identified differed from that of the first coronaviruses sampled in China by three variants, implying that none of the earliest patients represents the index case or gave rise to all human infections. However, multiple coronavirus infections in China, the USA and Europe harbored the progenitor genetic fingerprint in January 2020 and later, suggesting that the progenitor was spreading worldwide months before.

A recently published letter by Petti et al. summarizes existing evidence that corroborates the infectious disease epidemiology principle of pathogen circulation prior to the recognized outbreak [27]. The eventuality of an early SARS-CoV-2 circulation already relatively sustained in Europe and America is not so astonishing, as SARS-CoV-2 is mainly a respiratory pathogen. Therefore, a novel unknown respiratory virus responsible for severe pneumonia like SARS-CoV-2 could circulate undetected for months or years, be responsible for many deaths, and even become a pandemic, before peculiar characteristics of the disease are noticed that allow for its identification.

Looks as if the original virus that definitely came from China caused less severe symptoms and was not detected, but still caused infections thus antibody findings.

Did China do transparent peer-reviewed research into this?