That's because 2 Mishnayos back you already learned that these were exceptions.
כָּל קָרְבְּנוֹת הַצִּבּוּר אֵין בָּהֶם סְמִיכָה, חוּץ מִן הַפַּר הַבָּא עַל כָּל הַמִּצְוֹת, וְשָׂעִיר הַמִּשְׁתַּלֵּחַ. רַבִּי שִׁמְעוֹן אוֹמֵר, אַף שְׂעִירֵי עֲבוֹדָה זָרָה.:
None of the communal offerings require the laying on of hands except the bull that is ...
'ה never told אברהם to slaughter his son. Rather he was commanded to prepare his son ("bring him up") to be an offering i.e. bind him (see Rashi's comment on Bereishis 22:2).
Therefore it follows to refer to the event as "the binding of יצחק" because that was the actual test, to go up and bind him. Nothing more.