The calculation excluded the high results.
I have no idea of the sample sizes but ....
Say the main sample was 10t at 0.53g/t
Say the 643g/t sample was just 10kg.
The the overall grade if you include it is 64.7g/t
This is just playing with the numbers - and someone with a mining background like to suggest more realistic sample sizes. But this is a small mining op and the patches that contain grades like this one are certainly going to raise the average grades, as you can see above.
It will be the next update on processed ore that will blow the last of the 0.2c away.