Hello all, just reading up on some info regarding electronics on this very site.

Something cought my eye tho,
http://www.allaboutcircuits.com/vol_2/chpt_2/2.html
Why is the wave B considered a reference here ?

See screenshot provided aswell...

Granted I havent done assignments regarding vectors on AC in a year or so...
Anyone mind explaining why things are so ?

 

It is arbitrary. You, the designer, decide which one is reference.

In the case of these written materials. The person or persons who wrote them made that decision.