I guess it depends on the definition of a musical instrument. E.g. by Wiki’s standards it would be a correct statement.
There are of course people who would claim that a person would have to play the instrument in order for it to be considered as such. I do not agree, since there are plenty of bands out there that successfully have programmed entire albums (some have loads of them) on computers and never really played any of the instruments in question.
Take Vince Clarke, an original member of Depeche Mode, who subsequently founded Yazoo and Erasure. He’s a person who programs the music rather than playing it. I am not saying that he cannot play but that he, according to himself, makes the stuff by spending loads of time programming it.
I also think that there are instruments that are almost too simplistic to be compared to “real” instruments, and are rather non-musical and could fall into the same or similar category as a computer, e.g. claves, the triangle, a didgeridoo or drones in general, etc. Meaning, they make noise, some are a bit rhythmic, etc. but you don’t really “play” something, but rather complement the rest. Sure, you move your hands or lips and lungs, but no real melody, by measure of guitar or piano is generated.
Now, don’t get your underwear in a twist, I am merely trying to convey that I think instrument comes in so many shapes and sizes, but also in utility and usage, that I think one has to consider a computer to be some sort of a musical instrument. Even if one doesn’t actively “play” it.
Well, I guess that too is possible, by tapping the keys as a modern plastic replacement for claves.