That is indeed correct. However, it works only if your onward flight is the 777 and not the connection. We just completed a 2 week vacation in South of France with a 7 day cruise in the Mediterranean and our onward flights were EK505>EK75 and return flights were EK74->EK504. I was able to allocate row 6 on EK505 during online checkin but was unable to get any access to row 6 on EK504.

Sadly, EK74 is delayed by over 4 hours today and I will miss my connection to 504, so it wouldn't have helped anyway.