Most people can tell the difference between /naʊ/ and /nɑt/. I mean, just look at them... one ends with a consonant, one doesn't, and the vowels are reasonably different.
The difference here is between /faɪl/ and /ˈfaɪəɹ/, which is much more subtle. It comes down to the difference between /l/ and /əɹ/. The [ə] is an uncommon vowel in languages, unstressed, and mostly subsumed by nearby sounds. And worse, more than a billion people on the planet grew up speaking a language which doesn't distinguish the [l] and [ɹ] sounds (they're both approximants with only slight differences in articulation). So when you say "file" or "fire" these people can't distinguish which one you're saying, and when they say it they use something like the tap [ɾ] or retroflex [ɻ] instead, both of which sound ambiguous to native English speakers. Or some non-native speakers will use [l] exclusively, for both /l/ and /ɹ/.
FWIW, while Japanese doesn't distinguish L and R, "fire" is transliterated as ファイア faia while "file" is ファイル fairu. So the difference is reasonably clear.
The parent gave a phonetic explanation that has nothing to do with writing but rather hearing and speaking about it. For a billion people they aren't one letter away from each other, they're ~ the same. That's the point.
I am a bit embarrassed, but I had to read your comment twice to see that you mentioned two different products in your first sentence. So for me at least, GP comment is accurate.
Except "w" and "t" aren't similar in pronunciation. While "r" varies a lot in pronunciation across languages and regional dialects, there are many languages where the two ("r" and "l") require the same tongue position and a few languages where the two are (overly simplified) equivalent.
If you can discern between "now" and "not" then you can deal with "Firestore" and "Filestore"...