Yes it is. Nintendo is a monopoly with respect to licensing games for sale on Nintendo consoles. Monopoly is market-specific under US law, and the regulators can get very specific.
Regarding the first element, it is "settled law" that the offense of monopolization requires "the possession of monopoly power in the relevant market."(5) As discussed in chapter 2, monopoly power means substantial market power that is durable rather than fleeting--market power being the ability to raise prices profitability above those that would be charged in a competitive market.(6)
From the DOJ guidance on antitrust law (https://www.justice.gov/atr/competition-and-monopoly-single-...)
Regarding the first element, it is "settled law" that the offense of monopolization requires "the possession of monopoly power in the relevant market."(5) As discussed in chapter 2, monopoly power means substantial market power that is durable rather than fleeting--market power being the ability to raise prices profitability above those that would be charged in a competitive market.(6)