It was the exact advice given. Not all adverbs end in "-ly", either, and not all adverbs should be avoided in technical writing; that'd be impossible.

The rule states "-ly" words because those words are often cruft or crutch words that can be removed. If the sentence can't stand on its own without that word, then the sentence probably doesn't belong in the body of technical writing.

Compare this with time-related adverbs, which generally provide chronological structure. Those are more relevant for technical writing.

So yes, avoid "-ly" words. Not adverbs in general. That was the advice given.