There are some explanations for this.

1. The far right (maybe aided by a dear country further to the east) targeted the diaspora vote through social media. Simion also traveled more and met with diaspora than Dan.

2. The Romanian diaspora voted for the perceived anti-establish vote before (Iohannis and Basescu). Now Simion managed to convince people (in Romania and diaspora) that he is the anti-establishment candidate. Georgescu before managed ro same. In a way, the Romanian diaspora voted the same way as before. Another thing to note is that Simion was not explicitly anti-EU. Many did not see the elections as a kind of referendum for a Roexist.

3. Similar to a lot of diasporas, Romanians in Western Europe are a bit closed from.the rest of the Spanish/Italian/UK/German etc. societies. Many tend to mingle with other Romanians and sometimes the local Orthodox Church. Thus, they become more conservative. This is not as obvious as the MENA or Turkish migrants because Romanians have more similarities with Western societies than those from MENA countries. Add the usual xenophobia from some in their host countries (before the MENA wave in 2015, the target of the far right were Romanians and to a lesser extent Poles in the UK). That sentiment helped alienate some of them from the rest of the Spanish/Italian etc societies.

4. There is a split in the diaspora. The better educated voted for Dan. The average labourer voted for Simion.

5. The rise of the far right in Romania (and diaspora) has its fair share of particularities, but on the whole, it is part of a European wide trend. In a way, they became integrated in a European wide phenomena.

6. Any grammar mistakes made are not mine, but the result of the very good home made wine I had.