That's wrong in a couple ways:

• "Arabic numerals" aren't Arabic. They're Indian. They come from the Brahmi script, which is written left to right.

• The prevailing numeral system being replaced, Roman numerals, also placed the most significant digit on the left, so it's unlikely that this was something that was simply forgotten.

• Western languages (usually) mention the most significant digit first when reading the number out, which makes it convenient for it to be written that way as well.