As far as I can tell, Freebop is a combination of Free Jazz ("Free") and Bebop or Hard Bop ("bop"). Miles Davis's second quartet was certainly playing a hybrid of those two types of jazz at the time. Today that hybrid style of jazz is more frequently referred to as Post-bop, I believe to be a bit more all-encompassing for other artists recording similar jazz around that time.
However, as for Freebop specifically, Wikipedia has some information on why their music was called "freebop".
The quintet's approach to improvisation came to be known as "time no changes" or "freebop," because they abandoned the more conventional chord-change-based approach of bebop for a modal approach.
Unfortunately, I can't seem to find any contemporaries of Davis's Second Quintet specifically being called Freebop, but I have been able to find a few more modern jazz artists associating themselves with Freebop.
However, if you look at Freebop as a part of Post-bop, and are looking for artists within that subgenre, it seems to be much easier to find similar artists. Check out the Post-bop Wikipedia page (also linked above) for more information.