If I were attempting to explain it, I would start with how humans got to the planet in the first place. Given that most habitable planets are very far away, the humans travelling from one place to another would either need to have children in space, learn to travel very quickly or find a way to live much longer. The latter is where you can derive long life from by mentioning the science behind telomeres (which degrade as we age to the point of death), telomeres are sections of your DNA that protect all the important stuff, scientists have suggested that finding a way to halt or reverse the degradation of telomeres may hold the key to aging (at least in part).
Related reading: https://www.tasciences.com/what-is-a-telomere/
Once you have the long life as a result of youth you can then go further into the concept of DNA manipulation for space travel, talking about how muscles degrade in space, a solution to this could be to alter the DNA so that the muscle cells are more resistant to low gravity or even completely gravity independent. This would in turn mean that any landing space travellers would have a greater level of strength in comparison to the average human since most of your muscle mass comes from earths gravity and your need to resist it.
Related reading: https://www.nasa.gov/mission_pages/station/research/experiments/245.html
Now that we have established long life and great strength, you need a reason for the vampire population to require extra sustenance, you could justify this by creating a reason why the DNA treatment your humans received for space travel leaves their cells unstable, for example the muscle cells could require hormones or some other chemical to keep them afloat. If we go with hormones for the sake of an example, you could have one of the initial settlers developing a
hormone deficiency, requiring that they take the hormones from another by drinking blood etc, but once they drink the other settlers blood, the disease causing the hormone deficiency leads to the bitten settler developing the same deficiency.
The latter is quite sci-fi and will need some imaginative explanation but it's doable, in this example the long life could prevent dying completely (see: http://news.nationalgeographic.com/news/2009/01/090130-immortal-jellyfish-swarm.html), the muscular degradation due to a chemical deficiency would mean that drinking blood heightens strenght and not drinking it reduces strength to little more than an infant (see: http://www.nhs.uk/Conditions/Muscular-dystrophy/Pages/symptoms.aspx) and you could throw in explanations for multiple other abilities.
Other ability explanations include:
- Psychic - Cybernetic spinal chip implants, review the work of Professor Kevin Warwick for plausible explanations (see: http://www.kevinwarwick.com/project-cyborg-2-0/), although the professors work is still in its infancy in comparison to our examples, a neural implant and computer security could be used to explain breaking into someone's thoughts.
- Flying - Could be related to the muscular resistance to gravity, you could even have the cells generating gravity if you like (see: https://home.cern/topics/higgs-boson) using the higgs boson could give you a plausible excuse.
- Aversion to sunlight - Related to space travel again, chloroplast genetically inserted into cells to produce solar food for space travellers travelling vast distances, the muscle cells could produce excess carbon dioxide when not receiving enough of the chemicals that the vampires need to survive. (See: https://www.nature.com/scitable/topicpage/plant-cells-chloroplasts-and-cell-walls-14053956)
All of your vampires could have no idea why they are what they are, a hundred generations down the line from their space exploring ancestors they may have no concept of DNA modification etc. All of these traits could be developed naturally too, in the same way that the Turritopsis dohrnii developed its own immortality in nature, and the same way that plants developed their ability to digest sunlight.
I hope this helps!