rav - which is of the opinion that there is no zika, says the opposite here. shmuel, who said "yesh zika", says now the opinion of "ein zika" (not to rav ashi). this is very rare situation. couldn't [the opinions be consistent]?
Everyone agrees that "Yesh Zikah" or "Ein Zikah" is a Machlokes Tana'im, as RASHI and TOSFOS make clear (on 17b). Therefore, even if Rav or Shmuel holds l'Halachah like one Tana, he also must explain the reasoning of the Tana that argues.