The symptom described is typically referred to as an involuntary muscle spasm.
Unfortunately, it can be caused (when opioids are involved) by either active drug use or by an acute withdrawal syndrome.
In my experience, 90 days+ from discontinuing heroin is not usually a period of acute withdrawal. I have worked with addicts who transitioned to Suboxone or methadone and had continuing mild twitching/spasm effects. Is your boyfriend taking one of these?
My advice is to watch him carefully for any signs of dope use. Pinned pupils, scratching, slurring, money disappearing, etc. Hopefully, this is just a delayed withdrawal symptom.
And he should cut out the beer for now. Bad idea.