In US copyright law and most of the countries that adhere to the Berne Convention there is a concept of a derived work. What the legal standard is varies, usually a translation of a work of literature would qualify, but whether a "translation" of a work of software would be considered a derived work is an open question that will not be resolved without litigation.

But it certainly seems that this takedown is bogus in terms of the DMCA since it is not a copyrighted work itself, but an ( allegedly ) derived work.

It certainly looks like an attempt to misuse intellectual property law to protect a product from functional equivalents that would not otherwise be excludable from the market.