hey there, I am native Russian-speaker. If your question still bothers you, В and other prepositions tend to be pronouced together with the next word without pauses (as it is often done in English, too), so it can be a bit swallowed there and not distinct wnough. the sound itself is pretty similar to English 'v' but with less teeth
I don't think it's wrong, it's just not the usual way US EN refers to the метро. It works in UK EN.
he/she is going off Russian... ie the rough translation... Папа В Метро, dad is in metro/subway... it so mshould work but it isn't... the easiest way to learn Russian is to forget about 'the', 'is'(well not fully) and 'a'... so if it is Рюкзак в таски... just say 'Backpack in taxi'... as Russian drops most particles it mashes sense to do it this way... the rough translation makes lessening easier in my opinion because it goes straight to the basis of Russian which would be drop particles make is easy and simple(unless you're taking about grammar rules)
The official best solution is .. In the Subway, which is clearly wrong, Subway is a sandwich shop. It should be subway. But Tube, to my mind is understandable for UK EN, but is only, in reality, limited to London. Other places in the UK, where there is an underground railway use metro (for example, Newcastle).