We certainly saw a more caring side of Garnet in Garnet’s Universe. We also learned that Steven has a very large set of cartoons to draw inspiration from when constructing Garnet’s imaginary adventures, but as far as real lore we’re left looking.
The first thing we observe (the second if you count the springiness of Garnet’s hair!) is Garnet setting the bubbled gem aside so she can hold Steven, then the gem bubble floating in front of her. Gem bubbles have previously floated around when left unattended, so when the bubble moves it’s hard to tell if Garnet is controlling the bubble without using her hand or if the bubble will float more directions than just up to find a place it feels “comfortable”.
We know from Frybo and Secret Team that the gem bubbles require some concentration while being held, or the bubble will pop (coincidentally both of these bubbles contained gem shards rather than whole gems). Though Steven wasn’t able to distract Garnet enough to pop the bubble (nor was he likely trying), she still deliberately “sets” it aside rather than simply “dropping” it in front of her.
What does the scouter say?
In his fictional adventure he wrote for Garnet, Steven displayed an interesting perspective of her strength: while he regards her as able to overcome any challenge, he placed her as far too weak to do so without training (though the weighted hair shows he does consider her to have to ability to kick it up a notch in a fight).
It’s really hard to say what this might mean Steven thinks about Garnet’s strength. He could simply have made the observation that she always wins, and used the same script of “hero faces obstacle, hero grows to overcome obstacle” familiar from his cartoons without thinking much about it. It’s also possible that he’s simply aware that, as strong as she is, Garnet’s not the strongest force out there.
What it likely does not mean is that Steven has any good reason to believe that Gems can get stronger by training. His story sampled from many cartoons, and most viewers will recognize the Dragonball Z references, which include raising power level by an extreme training regimen. The Gems might still have the potential to raise their raw power, as opposed to learning how to use it better, but we still don’t have anything showing us that this is how Gems work.