No it wasn’t. Gerrymandering that demonstrably targeted racial or other protected demographics or otherwise broke the voting rights act was illegal. But gerrymandering as a concept has never been illegal in the US. State and federal courts, including SCOTUS, have ruled several times that there is no constitutional law against it, nor a mechanism to objectively identify it, nor a means to remedy it. If it violates those other laws in the process, it gets rejected and kicked back to be fixed. But if not, there is nothing illegal about it under current law, despite it being blatant vote manipulation.