That's not how Musk works at all. His method (proven time and time again with every company he is involved with) is to pick a massively unrealistic date and say it loudly and confidently to attract media attention and funding. There is no way that 2028 was realistic at all, ever. They are aiming for 2023 (which is still unlikely) for a fly around the moon. So 5 years after that an entire Mars base was meant to be built and supporting people? Not a single piece of equipment in that render has been created yet, so having it built, tested, launched, travelling for 8 months to Mars, landing, assembled and operational by 2028 would be more like something that happens in a movie where all of humanity have to concentrate solely on fleeing Earth because it is going to be hit by a rogue planet.