No, it's not. It was "adopted" by cloudflare, and although Mike Pall is a special person, there are other people who are contributors.

No, but it's forked: LuaJIT is compatible with Lua 5.1, and mostly compatible with 5.2), but not with 5.3.

Both Lua and LuaJIT are maintained and in active development.

LuaJIT != Lua