There are ways of faking GI, even with current techniques and without using ray tracing. Screenspace GI can look convincing (and also miserably fail). Radiosity

There are ways of faking GI, even with current techniques and without using ray tracing. Screenspace GI can look convincing (and also miserably fail). Radiosity techniques exist, etc. We've been able to fake global illumination for a while now. The results aren't perfect, but then again, that's what realtime computer graphics have been forever, a bunch of tricks that are close enough to reality, and 10 artists crying in the corner because they had to spend 5 hours moving an asset around so it looks just right.