I am not a lawyer, but I will bet you that the CA law is intended to apply to private conversations, not to a college lecture.
The last time I looked into this, there is a Supreme Court decision that we have a constitutional right to photograph, and video record anything which happens in public. This is why it is OK to record police so long as one does not interfere with their actions.
The college would have a very difficult time differentiating between a lecture at a public institution and a public event. Any argument that one has to pay tuition to attend the lecture is going to be tenuous in light of the fact that colleges encourage visitors, student guests, and prospective students to attend a few lectures to get an impression of what the college is like. This is always free. Sounds like a public event to me.
I suspect the school administrators are low-wattage drones who tried to misapply the law and got set straight by a real lawyer somewhere.
I agree, if I were a professor I would like my class to be video recorded. It would be a good way of resolving a student said / I said dispute. Also for security reasons.