English: “And if a goat is his offering” — this is a break in the subject, so that a goat shall not require the fat-tail.
In Sifra: After the sheep section (which demands the whole alyah), the Torah opens a new paragraph for the goat. That literary break is the derasha’s proof that goats have no fat-tail obligation, even though both are “flock.”
Type of Learning
Custom (paragraph break as exclusion of alyah for goats).
What Is Learned
Goat shelamim follow the cattle-style fat list (no alyah). Only sheep require the entire fat-tail to the backbone.