AXA Japan Fund grew after the Brexit referendum.... Why, because they are trading with the UK and UK parts are now cheaper? Err, no, it's a foreign asset, and we are measuring in pounds, so it became more expensive to buy.
Same with Korea
Same with Africa
And yes, same with the FTSE 100. The FTSE 100 contains companies like Shell, HSBC, BP, etc. Companies that have virtually all their assets outside of the UK, and those assets became much more valuable when measured in pounds post Brexit.
FTSE 100 when measured in USD however, performed much more poorly.
Likewise, the FTSE 250 when measured in GBP has risen constantly. The assets the companies hold outside of the UK are enough to give it a boost.
But when measured in USD, the FTSE 250 performed more poorly.