"To nejsou psi!"

Translation: Those are not dogs!

[CJMBenz]

Why ''psi'' and not ''psy''?

[tatka_]

Please read "Tips and notes":

https://www.duolingo.com/skill/cs/Animals

Nom. sg. - pes

Acc. sg. - psa

Nom. pl. - psi

Acc. pl. - psy

[SGuthrie0]

Why isn't it "ta", not "to"?
See this Tip: https://www.duolingo.com/skill/cs/Animals/tips-and-notesAnimals
Am I misunderstanding the Tip?