Now, I'm not taking one side or the other, here, but I think by "connected" he means joined, which implies that there's no isolation between earth-ground (E_GND) and circuit GND or COM. That answers your question, doesn't it?

Hos schematic has "gnd" on both sides of the optocoupler. STILL not told whether they are connected (directly or both to "net ground")

One of the areas where discussing schematics sometimes go astray is when "gnd" is not ground.

SO let me rephrase: how many ohms between the "gnd" at U1 and the "gnd" at R2

Erik