This question, and both answers so far, are endearingly naive and US-centered, if you pardon this opinion.
What they reflect is comparing a US system where (Trump's extreme aside), the actual policy differences between Democrats and Republican are fairly small. So, "Democratic in the US => left leaning in Peru and let's talk about stats".
The Peru situation
Peru is extremely different in terms of wealth if you are Indigenous
* (the people who voted for Castillo) and not Indigenous (the people who voted for Fujimori). You are talking the difference between obsessively swept streets and no-running-water districts, in the capital. Out of the big cities? Worse. Mostly split on ethnicity. To illustrate the degree of separation between the different people: Indigenous people, not infrequently, don't speak Spanish.
It has repeat problems of corruption at all levels of government. From politicians skipping the line to "experiment" the covid vaccine to getting involved in the Odebrecht Brazilian corruption from 3-4 years back. The politicians in question? Not-Indigenous, mostly.
It was caught up in a big civil war/insurgency problem in the 80s from the Shining Path. 75k dead, a terrorism-based war mostly sustained by Indigenous people seduced by a lunatic European Philosophy prof Marxist. Who didn't really hesitate at massacring them when it suited him.
Fujimori's dad presided over death squads during the war. But hers is not the choice of backing someone who has a recognizable Hitler-type ideology, it is backing someone who will oppose wealth transfer to Indigenous people. Possibly violently so, but I am still sure that a number of people were glad her father won the war, it had really not been a pretty one, even if the Indigenous populations suffered most.
Likewise, Castillo's party, if not necessarily Castillo (a political newcomer), is definitely not US-Democrats in flavor.
Quoting the Economist, June 10 (my emphasis and linking):
Assuming his victory is confirmed, Mr Castillo faces an almost impossible balancing act of trying to govern pragmatically for the majority while keeping his radical base happy. This week he showed his first clear sign of moderation. “We will be a government respectful of democracy, the current constitution…[and of] financial and economic stability,” he told jubilant supporters. If so, that may bring an early clash with his own party, Perú Libre. An avowedly Marxist-Leninist outfit, its founder and leader, Vladimir Cerrón, is a doctor who is an admirer of Cuban communism and Venezuela’s dictatorship.
So, in short you have the choice between a known-bad, continuity party, represented by Fujimori.
And Castillo's possible real "radical left", which is in any case going to pursue more equity for the Indigenous peoples (if he gets that past congress). At the level of existing inequality, that can't help needing to transfer wealth and services from the non-Indigenous population to the Indigenous population. In massive proportions.
(A remark about Castillo - he was a member of the self-defense peasant squads opposing Shining Path)
Now, don't get me wrong. The system as it is is both unjust and likely to cause further troubles down the line if steps are not taken to correct it.
But it is easy to see why Peruvians living abroad, who are likely not Indigenous, aren't going to back someone who, at best, will infringe on the privileges of non-Indigenous people in a big way.
And, at worst, might end up running a new Venezuela.
That is what makes this question about Dem vs Rep US voting patterns so parochial in nature.
The differences in choices are just much wider than what you see in Western elections and projecting US Dem => Castillo is pointless.
I hope Castillo surprises everyone and does a good job. Peru does need to address the gap between Indigenous and not-Indigenous. I fear it may not go well.