My ears hurt just from thinking about the vertical lobing that those spaced tweeters are gonna produce ...
My guess is that it's a "shaded array", with only one of the tweeters going all the way up, then another one going not as far up, and then the last two (probably the top and bottom tweeters) in play only in the lower part of the tweeter's range, all gently blended in. This would allow a crossover perhaps as much as an octave lower than would have been feasible with just one tweeter, and with less total change in directivity in the vertical dimension, but the same wide pattern in the horizontal dimension.