A Rebbe's vort

Mas. R"H 21A

Hichriz R' Yochanan:
R"Y made an announcement; That since it takes longer for Shluchim to get the message out about the Chodesh in Tishrei than in Nissan (because there is an extra day or three some years ((R"H & Y"K)) that they are not allowed to travel on), there are some cities that are right on the dividing line of one day and two day YomTov and therefore they get the message about the Chodesh in time for Pesach but not for Sukkos, they should still celebrate two days Pesach YomTov like the rest of Galus. Why? Because they might make a mistake come Sukkos and celebrate only one day, even though they hadn't heard from the Shluchei B"D, saying our custom is just one day just like we do on Pesach and possibly come to chilul Y"T.
One time two students of R"Y were visiting such a city and they saw them celebrate only one day Y"T and they didn't protest. When they returned to R'Y he heard about it and Ikpid.
They themselves celebrated two days when they were in that city, and you can be medayek that from Rashi D"H v'avdei chada yoma. Rashi wrights Bnei HaMakom the inhabitants.
Why didn't they say anything?
Possibly, since they were just visiting they didn't feel comfortable mixing in. Maybe the city had its own Rov that they didn't want to show up. Possibly the announcement by R'Y wasn't even widely known or accepted. The city wasn't even doing anything wrong. The Shluchim had shown up and told them what day Rosh Chodesh was! Because maybe by Tishrei they would make a mistake which even then might not lead to an Issur (if they guess correct). "Let's just mix out" they might have thought.
Ikpid Rebbi Yochanan.
They as Talmidim had a responsibility to mix in and educate the community.