No, those would be two digit courses. 1xx courses are typically for either undergrad or grad credit. 2xx courses are typically for grad credit. CS50 is the classic entry level CompSci course at Harvard.

https://www.seas.harvard.edu/academics/courses/computer-scie...

Do different Unis in the US use different numbering schemes?

Yes, while there are often some reused patterns (eg course 1xx being an intro course in many colleges) as we see here it certainly doesn't hold everywhere. For the most part there's no intercollegiate guarantee that bio150 at college X == bio150 at college Y.