[CraigS]

Yep.
Paper says:

"We estimate the likelihood of HVS3 being a (former) binary by looking at the complete survey of Brown et al. (2007b), who infer 96±20 3-4 M⊙ HVSs are located within 100 kpc of the Galactic center."

...(perhaps .... they do say "infer")... and then ...

"At least 14 unbound stars have now been discovered in a targeted survey for HVSs (Brown et al. 2006a,b, 2007a,b, 2009) and another 3-5 unbound stars discovered in other surveys (Edelmann et al. 2005; Hirsch et al. 2005; Heber et al. 2008; Tillich et al. 2009; Irrgang et al. 2010). Unlike high proper-motion pulsars, which are the remnants of supernova explosions, known HVSs are mostly B-type main-sequence stars (Fuentes et al. 2006; Bonanos et al. 2008; L ́opez-Morales & Bonanos 2008; Przybilla et al. 2008a,b)."
?
Article says:
"The team is now trying to determine the origins of four other hypervelocity stars on the fringes of the Milky Way. "We are targeting [other] massive B stars," says Brown."

? .. help ..! .. can massive B-types also come from supernovas? (My lack of star origins knowledge, showing here).

Appreciate comments.

Cheers
PS: Wiki says: fast neutron stars (from supernovas) don't have the HVS ejection mechanism. (?). Galaxy 'mergers' seems to be one belief. Currently believed to originate by close encounters of binary stars with the supermassive black hole in the centre of the Milky Way (& other galaxy cores).