Are muscle twitching, muscle atrophy, and leg weakness HIV ARS symptoms?

Unlikely HIV. These aren't common ways for ARS. The could be uncommon causes of end-stage HIV but even then it's not common to see just these symptoms. Muscle twitches and atrophy and according weakness of the affected side could be due to early age polio, impinged nerve in the spine or other nerve disease. It wouldn't normally occur bilaterally so I am guessing you mean just one side.