While there is a precedent for user-made content in console games like Little Big Planet and Super Mario Maker, this was never the case with mods in AAA games like the kind Bethesda produces, in spite of the vast communities centered around modding Skyrim and previous Fallout titles.
The reaction was surprise and elation on the behalf of the creative minds who have been modding games for years without much acknowledgement from the developers.
Back when Fallout 4 was the centerpiece of the Bethesda E3 2015 show, Todd Howard promised console gamers that they would also have access to mods, in just the same way as PC gamers would.