There's a specific geological term for that (I forget what it is) but it doesn't sound as impressive as "magma ocean".
All non-sedimentary rock was liquid at some point. They did simply find rock. It just so happens that they think this rock is exposed rock from the mantle. It's not like some volcano farted this out and that's somehow interesting. The word "ocean" also carries a lot of connotations that are not really applicable to a bunch of hot rock that was exposed by an impact. It's not like this was some pool of lava that was sloshing around up there.
You may not be the only one, but there's plenty of reason to believe they did this. For a start the West carefully tracks spacecraft trajectories using radar, the vehicle's transmissions are easily monitored (if not interpreted) using directional antennae and we can still do so for the orbiter, and surely did so for the landed vehicle on the earth facing side.
The vehicle on the far side is harder to verify, but it went into Lunar orbit and disappeared so it definitely went somewhere. Outing this as a fraud would have been trivially easy for many nations, plenty of independent scientists and even some amateur groups that have the gear and motivation to do so.
No you are not the only one. There are many people out there that believe the US and the USSR have fabricated their moon landing. And also plenty of groups that claim the earth is flat. You can find them easily with some quick googling.
I can't believe I'm saying this, but I think the flagged comment is a troll-troll.
There are streaks of self-awareness in that comment if you squint hard enough. This troll is clearly out to "sow" discord in the community, and he's being compensated for it in some manner. I say that because it's hard to arrive on any other conclusion -- why would he waste time on an audience like this of all places?
Rock. They found rock. No need to make water analogies for rock.