Asteroid 2012 LZ1 was discovered by Robert McNaught on the evening of the 12 June 2012. An asteroid moving past earth at 12 lunar distances is not necessarily noteworthy even for a potentially hazardous object (MOID= < 0.05AU).
What was noteworthy is the professional surveys have already found over 90% of objects over 1 klm wide, this one at 500-700m is very large for a new discovery, basically because it is in a highly inclined orbit and was detected at -61 Declination in the southern hemisphere - ie in Robert's favourite comet hunting territory.
What does this mean - basically that it is on a highly inclined orbit, not un-heard of but not common. The inclination is why it would not have been picked up as part of the more than 90% of big asteroids already detected, more commonly along the plane of the solar system.