Star Trek: Enterprise is NOT set in the same timeline as the TNG episode "Q Who"
In "Q Who", Q sends the Enterprise hurtling across space and forces them into an encounter with the Borg, to teach Jean Luc and the rest of Starfleet how woefully unprepared they are for what awaits them outside their quadrant of the galaxy.
Later, the timeline is changed in the movie First Contact, where the Borg go back in time to assimilate a defenceless Earth, and the Enterprise-E follows them. They succeed in helping Zefram Cochrane achieve warp speed and capture the Vulcans' attention, whilst also defeating the Borg, assuring Earth's continued existence.
However, this encounter changed the timeline in a big way. Zefram Cochrane got a good look at the "group of cybernetic creatures from the future who had intended to 'enslave the Human race'" and later described them in a speech. Additionally, two of the Borg drones ended up frozen in the Arctic circle, where they would lie dormant until excavated in the Star Trek: Enterprise episode "Regeneration".
The TNG episode "Q Who" that we see is in the timeline before it is changed in First Contact. The Enterprise episode "Regeneration" is in the new timeline.