סימנים וסימנים ועד אחד (Bava Metzia 28a)

From the gemara here (28a) it seems that an עד א' does not work by אבידה as the gemara says that סימנים וסימנים ועד א' עד א' כמאן דליתיה. However, the Rishonim (Ran, Ritva and others) in Chullin (96a) say that an עד א' is believed by אבידה.

One answer given is based on the מרדכי in the frst perek as follows. סימנים is like 2 עדים. Therefore when you have סימנים וסימנים ועד א' it is like you have 2 עדים vs. 3 עדים, and we all know that 2 עדים are equal to 100 עדים and therefore that is why here the עד א' כמאן דליתיה, he is the equivalent of a 3rd עד.