If I am not wrong, this is an antitrust suit, meaning it is about what they are selling, not what they are developing. If the product has been launched, there literally cannot be a monopoly.
They are both selling VR headsets. Claiming they are not competitors is like trying to claim electric cars are not in competition with gas powered cars because they are different technology.
Well.... I mean... we do consider trucks and cars to be different markets. And they are often the same technology. Same for passenger trucks to long haul trucks. Fundamentally same technology, but very different markets.