Ultimately, naming is pointing at clouds, but number theory IS older: https://books.google.com/ngrams/graph?content=graph+theory%2Cnumber+theory%2Clinear+algeb

Ultimately, naming is pointing at clouds, but number theory IS older: https://books.google.com/ngrams/graph?content=graph+theory%2Cnumber+theory%2Clinear+algebra&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cgraph%20theory%3B%2Cc0%3B.t1%3B%2Cnumber%20theory%3B%2Cc0%3B.t1%3B%2Clinear%20algebra%3B%2Cc0 https://books.google.com/ngrams/graph?content=graph+theory%2... Afterthought: I wonder what caused the decline in the 80's (also true for other branches of math)