Absolutely not obvious to me, especially since I have heard a lot of solo dev stories that insist it was purely a 1-person project. And it’s true in some cases.
In that case, please, define "developed the game" for us. Is doing all the programming "developing" the game? Is coming up with the game design and hiring programmers "developing" the game?
What if you hire voice actors for each of the characters? And level designers? And animators? At what point does it stop being a solo project? Only when outside investors get involved? Or does it only stop being "solo" if those investors demand board seats? Or can it _still_ be considered "solo" even then?