As someone with some knowledge in aviation, the mostly likely cause was pilot error. The weight and balance is taken care of prior to takeoff by the pilots at the 'gate', before taxi begins. This includes payload (passengers and their luggage) and the fuel load.
When landing, you're primarily managing speed and altitude. The slower you can approach the runway, the better, because that gives you more margin for error and it goes without saying that it's easier to stop a slower moving object than a faster moving object.
When landing the goal is for ~3.0-3.5 degrees of flare, and it's clear the plane had significantly more flare than that when it landed, although that doesn't guarantee a tailstrike.
What likely happened is the pilots got a bit too low, and/or had too great a rate of descent (referred to as vertical speed) as they approached the runway/touchdown, and flared a bit too hard, either to maintain altitude, or to reduce the rate of descent, making for a softer touchdown. Maybe both. As you approach the runway, nearly all airliners have altitude callouts, which are loud audio callouts of your current altitude above the ground by a robotic'ish voice in the flight-deck. Although they vary from company to company, these callouts generally occur at 1000, 500, 100, 50, 40, 30, 20, and 10 feet, respectively. So as the pilots approach touchdown they are precisely aware of their altitude above the ground.
The other variable in all of this is speed. As I said before, the lower the speed, the better (this is why flaps are deployed on the wing on approach/landing), they provide lift, allowing the plane to be functionally aerodynamic at lower speeds. Still, there is a critical speed that a plane must maintain in order to prevent stalling, a phenomenon that doesn't describe any kind of engine failure, but rather, describes a scenario in which the plane doesn't have sufficient lift; there isn't an equal amount of air flowing under and over the wings. This leads to a loss of aerodynamic viability and the plane begins to sink (or fall, if you will) in essentially an uncontrollable manner. Pilots have a specific landing speed to aim for, and the rule of thumb is that you should be +/- 5 knots of that specified landing speed. This speed is based on the weight of the aircraft and the selected flaps setting. This landing speed is generally sufficiently above your stall speed, and should you approach your stall speed, you will get audio warnings annunciated in the flight-deck, and should you begin to stall, the yoke begins to violently vibrate (called a "stick-shaker"). Furthermore, the speed you shouldn't fall below is clearly shown visually on the PFD (primary flight display).
The instinct of untrained pilots is to pull-up when in a stall, as common sense says 'I should pull back on the yoke as the ground is getting closer", when in reality, you should add engine power to provide lift. Given that these were at the very least commercial pilots, likely ATP Pilots, I would figure they were well versed in how to handle (and prevent) stalls, and I doubt they got anywhere close to stalling, although stranger things have happened, such as Air France 447.
At any rate, it seems the pilots could have handled the landing better but as they say, "any landing you can walk away from is a 'good' landing".
