Let's not get excited.
Farah would have had quite a bit of time off at the end of the track season and not focused on getting fit for this XC, meaning he isn't in great shape ATM.
Not to mention slogging it out on a muddy, hilly course isn't what Farah is good at and doesn't suit his bouncy style at all. He simply couldn't do his sprint finish due to the surface sapping his energy. Look how slow all the times were. Heath went early and built up a lead Farah didn't realise he couldn't close.
Heath is an XC beast, strong and works hard against the ground the whole way, expecting no return of energy from the mud.