I'm struggling to think of a conversion that would get "one" from 2600t to 5.6Mt (or T depending on what ElyDave said)
It's not just one order or magnitude out...
Lb to kg to ton(ne)s (or vice versa), a rounding error, and missing out a stage?
5600lb is 2540kg, 2600kg is 5732lb, so numbers above 2551(kg=5624lb) or below 5649(lb=2562kg) get us there.
(ETA - And I've just read the Guardian's correction, and reread Pingu's post, and it was 5.75 million tons. 5750lb is 2608kg. I bet the NASA press release says 5,750,000lb.)
(ETFA - That Guardian/Reuters story was published on 17th March, before the rocket's rollout began. The only press release directly on the rollout that's currently available on the NASA website is from 18th March, after the rollout had completed successfully. It gives the weight as 3.5 million lbs. That's not 2,600 tons.
However, a press release the day before says that once the rocket had been rolled out, they'll fuel it with 700,000 gallons of propellant (liquid hydrogen and oxygen). 700,000 US gallons is 2,649,788 litres.
While liquid oxygen is a bit denser than water, and liquid hydrogen is a lot less dense, what's the reckoning a time-pressed journo figured 'hey, a litre's a kilo,' rounded it to 2,600 tons, and missed the fact that's the weight of the fuel, not the weight of the rocket?)
(ETFFA - There's a Feb 3rd press release that says the rocket's weight is 5.75 million lb. FFS.)