Thirteenth-century Christian law tolerated Islam as subordinate religion, not heresy

Evidence

While the presentation of Muhammad in the Estoria de España would suggest that Islam would be a heresy, the Siete partidas, in accordance with thirteenth-century Canon law, gives the Muslims a subordinate but tolerated status equivalent to that of Jews, while denying any legal right to practice heresy. — John V. Tolan, Saracens, 980

Categorization

• QUESTION: Why did canon law distinguish Muslims as tolerated non-believers rather than heretics, given the theological case against Muhammad? This seems to track a pragmatic/political logic worth chasing.
• XREF: connects to: Canon law allowed rare family contact with converts to Islam