> ~47 million Americans aren’t native English speakers having immigrated from a non English speaking country.
Your link says 46M total which includes native speakers. So it does not state how many non-native speakers. (not that it would matter as most would be proficient english speakers, just pointing out you're exagerating and your numbers are wrong)
The question of your native language is answered long before any of what you’re talking about here. A 20 year old isn’t time traveling to have different parents when they take an exam.
You do realize they might be coming from another native-english country.
As such, your source is incorrect in that it's overly broad.
If you have an actual number then I'm curious, othewise it's ok to admit you were wrong and made assumptions.