i imagine they are referring to making hop tea usually utilised in k&k.
as for ag brewing hops would be boiled with the wort as normal practice, not sperately in water.
boiling in plain water works fine but you dont get the same level of utilisation as you do using wort.
ideally add dex or LDM at 10% of water volume to gain approx 1040 SG. This will give better results and adds to most brews without any adverse efffects.