The central idea that Brexit will harm BTC is not supported by the quote from Nicholas Gregory on which the article is based.

He says: ‘’Come 2020, we expect an increasingly populist and politically unstable world to cement the safe-haven status of Bitcoin and other cryptocurrencies…and if the central banks revert to ramping up the money printing all over again, the case for cryptocurrencies like Bitcoin whose supply is capped will be further reinforced.’’

He seems to think Brexit will in fact be a good thing for bitcoin.

Looking at the the same interview as reported by the Independent newspaper (way back in August) the meaning of his statement becomes much clearer.

Nicholas Gregory says: “Bitcoin has rediscovered its mojo this year with multiple mini surges but a no-deal Brexit could see a massive and unprecedented breakout. Not only will a no-deal departure from the EU create turmoil and volatility across two major fiat currencies, it will also trigger an identity crisis for the global system as the contingency and vulnerability of major global fiat currencies is laid bare.”

This is bullish news being reported as bearish by someone who is transparently trying to shill a bitcoin trading platform.

TL;DR: Clickbait, terrible journalism by someone who doesn't understand bitcoin.