Hortenzie, why not? What do you doubt? That footprints were made? That they were covered by sediment and so preserved. That shortly after they were exposed they eroded away? That they were discovered in that two week gap between exposure and erosion? It is true that is unlikely and that is why so few of these imprints are found, but there is no reason that it couldn't happen.
A more pertinent question is, perhaps, why classify these footprints as homo antecessor rather than some other type of hominid. The best that can be said is that they walked on two legs rather than four, the rest is guess-work. And the dating is based on similarities in sedimentology and palynology with another area which suggest they are part of the same complex of channel fills. Again we are talking of probability rather than certainty and it would have been better to express the headlines in those terms.