Thanks for sharing the link. You always want to be careful about finding "one" odd sample out of so many samples. They did mention the viral level is low. None of these tests is black and white. Many coronaviruses are so similar that they share large portions of their genomes. Since all the available tests are based on recognizing matching genomic sequences of these viruses (using antibodies or DNA polymerization), you may get false positive results when there are different types of coronaviruses present in their samples. Especially when you detect something at a borderline level, you want to extra careful. It may very well be simply another kind of coronavirus.
Also, if the virus actually has spread in that area in Spain back in March, 2019, I would expect to see steadily increasing levels of viruses in that area. And they should be able to detect the virus in other samples collected in the same area. Labs in Houston have been conducting experiments of measuring virus levels in sewages throughout Houston since May, 2020. They have consistently found that viral levels detected in the sewage is a good sign of the level of infected in that particular area. I believe, since September, city of Houston has been using sewage samples to identify the heavily infected areas in Houston. This is, of course, a non-intrusive way to keep track of where the infections are. This means that you should consistently detect viruses in sewage samples, instead of just finding one odd sample.
I would not be surprised that the definitive origin of SARS-CoV-2 originated somewhere else. As I mentioned earlier, these viruses usually take years, sometimes decades, to jump from animals to human. It takes them a long time to gather necessary mutations so that they can transmit from human to human. So it's not surprising to me at all if they, one day, find a very similar virus somewhere else in the world. It may simply be an early attempt of this virus to jump on a human, but most likely failed to jump to another human. With that being said, literally tons of irrefutable evidence demonstrates with no doubt whatsoever that the viral strains causing the current pandemic came out of China. Nothing at this time will change that.