Is VIN the same as VCC?
Nomenclature is always a problem, so sometimes one has to make a good guess. That HMC5883L requires a DC supply voltage. Does your module seem to have an on-board battery?...no?...then the DC supply likely comes from an external source. The pin labeled "GND" is required by the serial link (SDA,SCL) for data communication, but it can also be the ground return of this external source.
 Another clue comes from the similarity of pin nomenclature to your tutorial photo. The only one that differs is "VIN" vs. "Vcc". You are thinking intelligently in relating these two.
 Since power is likely supplied from an external source to this module, it is reasonable to say that this is an input pin. It inputs voltage to the module. Silk-screen labels must be short, so these cryptic labels are ubiquitous.
Some more info on "Vcc":What is the difference between \$V_{CC}\$, \$V_{DD}\$, \$V_{EE}\$, \$V_{SS}\$