I don't think that this would be altogether surprising. The 388 is well-known for having only very limited cargo capacity (one aspect, AIUI, of its generally payload-restricted characteristics). That, it seems, is a factor in why BA operates a 388 alongside a 77W on both HKG and SIN - the 77W is a real cargo monster even when the pax load is high, and that's one of the reasons why the 77W turned out to be a roaring commercial success for Boeing.

As its shape suggests, the 388 could almost be thought of as a shrink from what the aircraft was envisaged to end up being. IIRC, if it had been stretched into a notional "389" or beyond, cargo capacity would have increased disproportionately. But we will now never find out.