Its a real Arisaka.
In order to be a counterfeit / fake it would have to be presented as something that it is not, and as far as I can see, it was just represented as an Arisaka, which, it is.
While I'm not an Arisaka collector, I know that there are some ultra rare variants that are worth considerable money, and were valuable, even when the standards rifles were dirt cheap.
The OP's gun isn't pretending to be one of those.
Some forgers/counterfeiters are smart and crafty, some less so...
With guns, counterfeit markings to fake a more valuable version is most common, and while I don't know of any cases where a gun was made from scratch to counterfeit a valuable gun there might have been some. WHY anyone would I don't know other than the expectation of significant profit.
Sometimes, that expectation goes unrealized. Two storied about counterfeiters who were less than brilliant come to mind.
First one, the Feds found a guy who was counterfeiting $1 bills. No other denomination, just $1 bills. The Fed watched him for years, learned how he did it, but never prosecuted him, because they learned it was costing him $1.06 to create each fake $1 bill. Some Feds DO have a sense of humor.
The other one was a guy who was making fake $5. He was cutting Lincoln's picture out of a real $5, pasting it on a $1 and running them through a change machine (that took them) and getting $5 in change. So he was spending $6 to steal $5! They did bust him, though I think the charge was felony stupid, more than counterfeiting.