Turns out the one spreading the rumors was Hashimoto, who did so at the behest of Sakayanagi. Shortly thereafter, Sakayanagi appears before Class C and she informs them she has evidence regarding the rumors about Ichinose.
Oh, th-that's funny...
...هـ-هذا غريب
Ay, qué raro.
Qué rara soy.
Tiens ? C’est bizarre.
Oh, isso é engraçado...
Ой, странно как-то…