Pliny on the formation of the Gibraltar Strait

Earliest cultures inhabiting southern Spain had their own saying on how the Gibraltar Strait was formed, and it was not so different from today's!  Here comes some kind of Mediterranean refill theory as accounted by Pliny:
"At the narrowest part of the Straits, there are mountains placed to form barriers to the entrance on either side, Abyla in Africa, and Calpe [present Gibraltar Rock] in Europe, the boundaries formerly of the labours of Hercules. Hence it is that the inhabitants have called them the Columns of that god; they also believe that they were dug through by him; upon which the sea, which was before excluded, gained admission, and so changed the face of nature."
From Pliny's Historia Naturalis, vol. 3 (preface), ~77 AD

Amazing, ha? Was this anticipation of the flooding theory of the Mediterranean inspired by evidences that suggest a desiccation of the Mediterranean such as the widespread presence of salt we see today? Or was just inspired by the strong inflow currents well known by sailors at that time?