It's possible:
* The term is being used informally or within a specific context: Someone might use "cardinal" to describe a dominant or important school of thought, emphasizing its central or key position. Without more information on where you encountered this term, it's impossible to say what it means in that specific instance.
* It's a misunderstanding or misremembering: The term might be confused with another philosophical or theological school. Perhaps you're thinking of a school that emphasizes certain key principles or figures (which might be considered "cardinal" in the sense of being essential).
* It's a newly coined term: Someone might have recently created this term within a particular academic or philosophical discussion.
To understand what "cardinal school of thought" refers to, you'd need to provide the source where you encountered the term. This would give context and allow for a more accurate interpretation.