Brainfuck has 8 opcodes, while flipjump (like subleq) has 1 opcode

As C and Subleq aren't turing complete, it isn't too. Yet it can do somehow effectively any computation your cpu can as it can do and, not, and memory accesses. It seems to actually implement many of the usefull operations in its standard library

Well not exactly, as turing completeness requires infinite memory, and the subleq operands are of finite sizes (and so the addresses they addresses). But, it's like C isn't realy TC as the basic types in it are bounded by there sizes. Your computer doesn't need TC, as it has a finite size too.

But is it though? I once read you can implement infinite memory address register with it, Ill look it up

What about it?

This language has one opcode that flips a bit and jumps. The creator built a standard library and created a calculator, pointers, functions. Its the most simple OISC that I know of.