There is an exciting new theory about early Earth. Rather than having a liquid metal core, the Earth has a liquid water-based core. And the Earth was much smaller in diameter back then, with a non-watery crustal surface. As the core heated, the liquid water core released steam which broke through the crustal surface and created rifts which drove the continents apart, and spurting water from below created the oceans. Gravity was lesser than now when the dinosaurs roamed the Earth, calculations taking into account a different core than now. The Earth expanded like a balloon over millions of years, and gravity increased to what it is now. These theories came about due to experiments on rotating droplets of water done by astronauts in space. Non-liquid particles move to the outside surface while the water stays in the core, the water heats and hot steam bubbles remain in the core, expanding the droplet.
As you say, we can only speculate. But scientists always get whiplash when new evidence makes them toss out their old theories that were thought to be "facts". They still don't truly know what happened.
If you believe that nonsense news story at face value, you’ll believe anything. Whoever authored that news story took a few actual events and invented a whole fantasy around them that has practically nothing to do with actual natural history. The comment, “Gravity was lesser than now when the dinosaurs roamed the Earth....”, is particularly laughable. They take the fact that the Earth has accreted almost negligible mass from meteorites, asteroids, and comets impacting the Earth during the last 200 million years and ignore the almost negligible losses of mass to outer space as gas from the upper atmosphere is stripped off by the Solar Wind and propelled to the outer Solar System. The overall gravity of the Earth has undergone no significant sized changes since the beginning of the age of the dinosaurs. In fact, the last significant change in the Earth’s gravity occurred when the Earth was reformed and the Moon was formed by Earth’s collision with another mars sized planet in the very early stages of the Earth’s existence more than 3 billion years ago.