Someone who just disregards a past psak without a problem is not worthy of being a Rav.
Feh… all that boils down to is “we must obey the past.”
Is it possible that maybe he did regard R. Moshe’s p’sak and came to the conclusion that:
(a) Maybe R. Moshe’s ruling was based on incorrect facts
(b) Maybe conditions have changed since R. Moshe’s ruling
(c) Maybe others have put forth reasons to allow an eruv that R. Moshe did not consider.
Or perhaps there is some other reason. In short, just because someone disagrees with a rav’s p’sak doesn’t mean that he disregarded that rav.
The Wolf