1: A small sample size is perfectly fine for the claims their making, which is just that they've detected micro plastics for the first time.

2: It says it in the linked study

Tissue samples were extracted from six individuals who underwent surgery for a multi-component inflatable penile prosthesis (IPP). Samples were obtained from the corpora using Adson forceps before corporotomy dilation and device implantation and placed into cleaned glassware. A control sample was collected and stored in a McKesson specimen plastic container.