Ah their marketing says it's so. Then it must be true
Just like all those blurple claims must be true?
Besides, they blatantly lie about the output of the "lamp" as well. It's not emitting 2umol/s/W. Probably more like 1.6umol/s/W.
Again, their actual specs don't claim it's at the same efficiency. Just that it's around this supposed 2umol/s/W both at 600W and 750W, but their 1000W fixture is also slightly more efficient at 1150W over 1000W It's obvious that the same goes for their 750W fixture. Going by the difference on the 1000W model it will be a 4% difference in efficacy between 600W and 825W. While at both wattage's it would still be rounded to 2.0umol/s/W for the bare bulb measurement.
So even if the specs and marketing are not 100% incorrect, 4% is still a decent difference.