Surprised to see that any EK pilot would even consider to fly Vnav of FLTchange during a small change in level/ alt.
Basic Airmanship gentlemen?!
For small altitude changes, less than say 3000', use VS and avoid large thrust changes, large cabin attitude changes, risk of TCAS events, more room to correct Atc reclearances,...
This is taught DAY 1 of line- training ab-initios!
I remember being told that an undocumented feature of the 757 and 767 FLCH logic would limit the RoC/D if it could reach the selected altitude/FL within 2 minutes. Made for lovely cruise climbs/descents compared to chucking it in the box and letting VNAV throw all the power on and avoided the risk that a numpty would forget the relationship between the VS pitch mode and speed at high altitude. Does the 777 not have this feature?