This is a reboot with new characters, for instance Bill Murray made a cameo but not as Peter Venkman , Burk is correct, the sequels had the original cast as there original character's , This movie had new characters thus reboot.
so why would a ghostbusters movie have the same actors from another ghostbusters movie?
then another ghostbusters movie had the same actors from ghostbusters 2 but that movie isnt called a reboot. even though there are new ghostbusters in it. the other ghostbusters show up as cameos as the movie was not about them but the new ghostbusters.