Somebody must have told them a new gun name they'd never heard of and they thought it sounded cool. With all the crappy contraditory info floating around, they can't even decide what the vehicle looks like, or if the driver(s) are hispanic or islamic.
I seriously doubt that anyone has accurately seen the weapon well enough to make that call. If it was an AK-74, most people would mistake that for an AK-47 anyway, if they were even savvy enough to recognize the outlines of a Kalishnakov.
IT doesn't explain the ATF showing a bunch of AR-15's and HK .223's about a week ago saying "These could be the types of gun the sniper is using."
A .223 is not a 5.45 x 39MM
Well the Kalishnakov profile is very well known. So maybe they showed the witness pictures of various guns that could fire a high velocity approximately .22 caliber round, and he picked the AK of which ever type. Maybe it's one chambered in .223/5.56 NATO, maybe one chambered in 5.45x39? There is a different in the shape of the magazine (note that M-16/AR-15 magazines are straight, whereas AK-47 and AK-74 magazines (in 5.45x39) are curved "banana clips". This is due to the shape of the catridge, (7.62 NATO magazines are straight too, even the 30 round ones). Maybe the picture the witness ID'd had a curved magazine, but since both Chinese -47s and Russian (and other) -74s are available in both 5.45 and 5.56, maybe not too.