Beldar does kind of look like mine (unnamed ATM) ! But I do notice his head is more cone shaped and his tentacles are spotted all over and mine is paleish! I'm pretty positive u were right calling him an o.briareus
The problem (or one of them ) with trying to ID even a common octopus is their changability and ability to look like things around them and, to some degree, each other at any given instance. As you see more of him/her more it will become more obvious but a single picture can be deceiving. I included the other slight possibility because I have seen the Macropus look very briareus like in some colorations and the LSF thought it was Indonesian but I'll bet the farm on O.briareus.
I ruled out O.vulgaris with Little Bit because she grew too slowly but, in the end, was sure that was her species even though she stayed small (she grew way too large for similar looking the alternative). I am having similar issues with Yeti. I have raised a number of O. briareus and two that hatched in my tank. Yeti looks every bit like a very young O. briareus (I would have bet the farm without hesitation as I KNOW where Yeti was caught) but she/he is still tiny with little growth at a time she should be growing exponentially. The O. briareus link above and the one he kept prior never reached the size of the ones we typically see (but lived normal life spans) so I don't know if Yeti is just going to be small OR there is another species that looks identicle as a hatchling. Fun stuff