As one can imagine, it was easily possible for the person doing the scanning to turn two pages, when they only meant to turn one.
The evidence from the online returns available demonstrate that this is precisely what happened. If you look at the return for James Lynnott, you can see from the bent over rear corner of the preceding page, that that page was a house return page, rather than a building return. So the 1901 return for the Naughton family does exist, it was simply unscanned.
I would also note that I believe the 1901 census was only scanned once, so the images on the NAI, FS and Ancestry sites all have the same origin, so an error on one is an error on all (at the scanning level).
