True... for example, I would bet money that if you showed him a photograph of a bird from the genus
Passer ...
...and asked him
Что это такое?, he would answer
Это маленькая птица ("It's a small bird") or something close to that, whereas most Russian children over the age of five or six would answer
Это воробей ("It's a
sparrow").
Or, if you asked him how to say "Those people are very wealthy" in Russian, he might be able to provide a direct literal translation like
Эти люди очень богатые, but it would never occur to him to say
У них всё есть, кроме птичьего молока, ("They've got everything but bird milk") because he was too busy learning Hebrew, Catalan, Afrikaans, etc., to study Russian in more depth and learn some common proverbs and figures of speech.
Which is to say that "fluency" can be defined in different ways, and the BBC video shows that he has an impressive ability to master different accents and perhaps also an excellent memory for rehearsed phrases, but he's not actually demonstrating an ability to converse fluently in all those different languages. (Maybe he can, but the video doesn't prove this.)