If he didn't use the 1080p TV and only had the 4K, then 1 of the following would happen:
1 black screen
2 1080p playback
3 4K playback
if he got (2), he wouldn't be able to tell if the problem was with (HDCP+4K) or just (4K). Proving that it works in 1080p on a TV that doesn't even know what 4K is establishes the baseline and eliminates the ambiguity.
1 black screen
2 1080p playback
3 4K playback
if he got (2), he wouldn't be able to tell if the problem was with (HDCP+4K) or just (4K). Proving that it works in 1080p on a TV that doesn't even know what 4K is establishes the baseline and eliminates the ambiguity.