To my opinion this could be territorial behaviour between two males. In mating behaviour males clasps females from the belly side; in territorial behaviour males claps each other from the dorsal side. Although there is much discussion about if this behaviour is territorial, I am convinced that it is, because salamanders have excellent smell and can distinguish between males and females, but...sadly not much research on it has been done. Up un til now it has been observed in S.s. gallaica (by mr. Bas-Lopez), S. s. salamandra (by W. Kästle is remember correctly) and in S. algira tingitana (myself)