Probably disagree a bit with Guideboatguy. Overall more hull in the water proportionate to the paddler’s weight should increase stability, but I can name kayaks at 17 feet that would have put you in the water as fast or faster than the Rio did because there are so many factors to a kayak design as well as the paddler interacting with it.
And you are also at the top of the weight range for that boat. It is specifically designed per the manufacturer’s page for the small to medium paddler. In fact their web site shows a female paddling it. You are a medium sized paddler, and well may be sinking the boat to its optimal waterline just sitting in it without gear. A kayak that goes past that waterline gets more unstable, for example that is why you usually get the extra water out of a kayak in an assisted rescue. A waterlogged kayak is too deep in the water hence unstable and extremely likely to capsize again.
But the biggest issue for new paddlers.in a kayak is not understanding that the boat is supposed to be wiggling under them. So you loosen up your hips and let it do so without affecting your center of balance. But if you stiffen up so that your entire torso is going over side to side as well, it is only a matter of time before you will be taking a swim. Especially if you are already at the top of the intended weight for the boat…
The Rio likely does what any other kayak designed for this market should do, which is to be inclined to stop at a certain point before fully capsizing. If you are on the lighter side compared to the boat’s intended paddler, or if you stay relaxed and centered, it will do that. If you are pushing it on size and/or tense so you cannot absorb the motion, it’ll keep going.
The problem for a lot of new paddlers - and many here have gone thru this - is that they choose a first boat based on how “stable” it feels to them when they start. Then they paddle it for a few weeks or a season, get used to the behavior and relax, and find they have the wrong boat. The original challenging boat is slow, boring and not what they want longer term. Hence peoples’ common recommendation to start out buying used and/or take some lessons, to get all of that out of the way without breaking the bank for a new boat that you want to get rid of 8 weeks later.