Remember Stuxnet? Hack one of these, wait until the right compounds are physically loaded, then execute https://www.sigmaaldrich.com/US/en/products/chemistry-and-bi...
I don't think the grandparent was implying the AI would be controlling robot arms to mix things directly (or at least I didn't interpret as such), but it could very well sit in the network until it notices two dangerous compounds in the same machine, and trigger a breakage that causes a harmful mixture. Break a vial containing a virus, then break two more that cause an emergency evac and maybe that's enough to get something out there.