My biltong has white bits on it – is it mould?

The white bits are unlikely to be mould due to the nature in which the product is produced.  The white bits are likely to be some of the salt used to marinate the product trying to rehydrate due to humidity.  This poses no danger to product consumption, but if you don’t like the look of it just wipe the price with a little cider vinegar and it should go away.