Means of production is not solely a factory. To produce requires energy most times, so another means of production, besides the factory floor, would be an energy source. That could be an electric generation station or perhaps an oil field and its refining facilities.

My feeling is the Marxist want to seize the means of productions so that wealth can be more evenly disbursed. Envy does not seem a big part of it in their literature. No part, in fact, from my non-extensive research.