Islam Critiqued is a true linguist; foreign words in Arabic?

In answer to the video "Top 10 Ways Muslims Ignore the Quran"

Polemicists have misconstrued a known linguistic phenomenon so as to try another weak attack against the Quran. To enforce their obsessive claims of borrowing, they have scavenged the book for supposedly "foreign" words. These words betray the Quran's adoption of foreing concepts, as well as the fact it needed additional vocabulary to express new ideas.
Firstly, all languages, including Arabic, have eventually adopted foreign words as people have interracted. Sometimes these words retain their implicit cultural or theological baggage. At other times a completely new meaning is assumed.

In the Quran's case, foreign words do not even amount to a fraction of the totality. In addition, many of those words pointed to by the critics either are in fact Arabic, with well established triliteral Arabic roots, or have been part of Arabic vocabulary since before the emergence of the prophet, or were common to other Semitic cognate languages of the region, thus rendering their tracing very difficult.
Recently for instance, Wolf Leslau refuted Nöldeke's identification of certain Arabic words in the Quran as Ethiopic, like shaytan or jahannam, proving that the direction of borrowing was actually the opposite. The words that entered the Arabic language prior to revelation cannot be termed foreign. They are now Arabic words.
Onus is on the critics to prove that these words were borrowed post Islam. Anyone familiar with pre-islamic literature and poems knows how rich and expressive the language of the time already was. There was no need to express any of its ideas by borrowing foreign words. In fact none of the supposed words or expression do not have their synonym, either in other passages of the Quran, or in the well established Arabic language.
In any case, whether a Quranic word truly is originally foreign to Arabic and in addition retains its original meaning, by becoming part of Arabic vocabulary and common use it necessarily, as in any language, becomes an Arabic word.