Maybe some real world numbers will help you understand whats going on.
I'm running 10 Samsung 2' LT-Q562 strips with a MW HLG-240H-24B driver (Smaller driver and less strips then the article you are quoting). I have the adjustable potentiometer on it with a digital readout of voltage, current, and wattage going to the lights. I have switches so I can turn on and off the lights individually if I wanted, I just turn down the wattage accordingly.
Here are ACTUAL readings from my light with all 10 LED strips on (40 LED/strip);
100.8w = 22.21V @ 4.54A = 0.454A/strip = 10.08w/strip = 0.252w/LED
200.4w = 23.17V @ 8.65A = 0.865A/strip = 20.04w/strip = 0.501w/LED
240.7w = 23.53V @ 10.23A = 1.023A/strip = 24.07w/strip = 0.602w/LED
I believe (I may be wrong) that the Samsung rated max for the LT-Q562 is 1.2A (it use to be 0.900A but they increased it)
I typically run my lights at 200W (0.865W/strip) = 72% of Samsungs rated max for the strip.
For reference the HLG 288v2 (301b diodes) (
https://horticulturelightinggroup.com/c ... v2-led-kit) runs a max of 150w/288LED's = 0.521w/LED. That's a little more then I typically run at (0.501w/LED). If you were to run the 18 2' strips of LT-Q562A with the HLG-320-24B driver your max would be 0.444W/LED.
If you max out the HLG-320H-24B driver on 18 strips it's 17.777W/strip, that's lower then I typically run. The HLG-320H-24B is a CV driver, if you dial it down it's a CC/CV driver that runs a curve. You can run it with a single strip but you'd be powering that single strip at absolute max that the strip could take, this would generate a lot more heat (fire risk), reduce the lights efficiency, and shorten the lights life. You can turn the potentiometer way down and run only a few lights (one light is still probably unrealistic and unsafe for such a large driver).
The article on the build looks to be a good one, if you follow it should should be fine (I didn't write the article and use the information at your own risk)