Contagious?

Lilia has a best friend: Amine. Amine's parents are from Algeria, so he speaks "Maghreb" (this mixture of Arabic and French). He also goes to school, which obviously means he speaks English.

When they play, they usually speak Arabic, which is what I would expect them to do.

Every now and again, though, Lilia says something to him in German.

The funny thing about it is that he seems to understand her! The other day she asked him to do something, and he replied "Ok" and did it.

I don't think he's going to be able to speak German, but I wouldn't be surprised if someday he realises that he has no trouble learning it at all.

So is "being multilingual" contagious?