It sure looks like a cast iron flange and drain pipe. These are typically bonded together with poured liquid lead onto a packed oakum seal. Several ways to remove it. One way is to drill holes in the lead, pry it out, then pull the old flange off. Another is to whack it with a hammer and chisel to break it (best left to someone who has done it before!). Then, the best thing is to pour a new CI flange, but there are other choices.