Ryde doesn't call the ZAC19 rim specifically a "lightweight" rim. It's a part of their "Standard" range, which "varies from lightweight mountainbike rims to heavy duty aluminium rims and almost indestructible stainless steel rims." (The Rival models in that range actually do get called "lightweight" by Ryde.)

The extrusion looks pretty beefy to me, sort of like the Sun CR18, which also shares a very obviously conservative tension rating.