The following is
(more or less)
Most Spanish nouns have gender. Thus, you can translate "friend" as "amigo" if it is a male friend or as "amiga" if it is a female friend. Plural nouns are the same, so you can talk about "amigos" or "amigas". But there is a catch. If among the group of female friends one has a male friend, then the plural is "amigos" like if all the friends were males.
Moreover, in Spanish there is a hint of machismo. We don't have a neuter term like "siblings", we talk about "brothers", even if there is one brother and five sisters. We don't have a term like "children", we say "sons". We don't have a term like "parents", we say "fathers". And so on.
We Mexicans like to copy trends from Americans, and political-correctness is not an exception. Now, some people talk about "amigos y amigas" instead of just "amigos". Since this is more cumbersome than the English "he/she", using the "@", like in "amig@s", is becoming more common.
In conclusion, I can understand the use of "they" instead of "he/she". Although I prefer some less confusing term like "s/he" or something similar.
I step down from the soda box.