But the Penei Yehoshua explains that even before this incident, R’ Yossi knew that it was assur to enter a Churvah:
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It seems that the only thing Eliyahu taught him was that the concern of Mazaikin overrides the issue of Bitul Tefilla, although technically you can perhaps read it as saying that Eliyahu was mechadesh the issue of Mazikin but I don’t think that’s what it’s saying.