CVT’s need specific fluid, and if your mechanic used the ATF for regular Honda transmissions, then it is very likely that this caused the failure of your transmission. CVT’s are somewhat new (actually re-surging), so we don’t know what their life expectancy is, but with proper maintenance they should be fine.
Now, getting your mechanic to pay for the repair might be difficult. You have all the receipts? Try talking to him and see what he says. If he has good insurance, you might get somewhere. You could look into small claims court.