Few thoughts...
Yes, the rumors were true, much like most you hear in CX over and over that seem to make sense.
It makes sense because the cargo market has been down for some time now and the last thing CX needs is a huge investment in 8 777Fs.
ACC does need them because the -400BCFs are killing the JV during this prolonged, down cargo market. Their loads factors have been quite weak. Therefore, the 777F's smaller size makes sense for them.
Despite the weakness, CX has been able to keep load factors to NAM quite high by canceling and consolidating flights. The -8F is great for this because it can carry 130T across the pond if required.
This buy takes the -8 fleet to 13. Clearly, CX likes the performance. Accordingly, I think this brings us one step closer to a -8I order. There is confirmation that the airplane is appreciated, perhaps even more so than the 777F would be.
The fact that CX can get -8Is by next year, or even the end of this year, makes it attractive vs the A380 with longer wait times. This could help CX get more aggressive retiring -400s, which they seem keen to do.