Hello,
People is me.
Yes, but not that it is mandatory.
No, what I 'used' is :
RQG p76: Lhankor Mhy cultists may start with up to five points of cult spirit magic or up to three cult sorcery spells. (emphasis not mine, but RAW).
RQG p76: Cultists trained in sorcery start as having mastered the principles of the Truth Rune and the technique of Command (see page 381).
RQG p73: If your cult teaches sorcery, you may start with up to three sorcery spells from the cult’s list. If this option is taken, you do not start with any cult spirit magic.
The 'Cultists trained' means that there are some that are not, and the 'or' means that you can have only one of the two at character creation time.
As I already explained, yes, I agree with you ... at world level, but not at rules level.