They're very like the Bilbao we lost to, aren't they?
A similar style, yes. Not surprising as Berizzo served under Bielsa as a player and an assistant. Decent article here on Celta's strengths, weaknesses and style of play:
Celta boss Eduardo Berizzo looked to compatriot Marcelo Biesla for inspiration and advice. His side will try and play like Bielsa’s Athletic Bilbao side which knocked United out of the 2011-12 Europa League, with a fast counter-attacking style using combative players who operate a zonal marking system defensively. Celta have already beaten Barcelona and Madrid at home this season - and been hammered 5-0 by Barça away.
Berizzo makes good use of his substitutes; he doesn’t have a settled starting XI and his formation usually resembles a 4-2-3-1.
http://www.dailypost.co.uk/sport/football/football-news/who-manchester-united-fcs-opponents-12980805