Did California used to be part of baja California ?

Not quiet.  During Spanish Rule there was a single vast province called Las Californias.  After Mexican Independence the province was split into two parts:  Baja California (Lower California) and Alta California (Upper California) with the dividing line running more or less along the present US-Mexican border.  

Of the two the Baja California was more settled.  While the Spanish explored the coast of the Alta California as early as 1542, they didn't really explore the interior until the Portola Expedition in 1769.  Besides exploration the expedition established twenty one missions in Alta California, which had grown into major California cities.

It was all Mexico 200 years ago.

California was Alta California to distinguish it from Baja California