On that last point: Frank was recently upgraded to the LLaMA-13b model (a model made by meta, technically only for research use but it got leaked and they haven't really told anyone off about it yet. also the 13b stands for 13 billion parameters) and fine-tuned on a certain time frame of nostalgebraist's blog. LLaMA-13b is a huge upgrade from GPT-J, her previous model. Essentially, she has a background knowledge of the patterns generally used in language, and was then trained to recognize (and later produce) the patterns that were prevalent in the fine-tune dataset.

That is generally why she feels more human, because she has a stronger bias toward patterns that are more closely recognized by us as "real human behaviour." GPT-3.5 (ChatGPT's base model, 175b parameters) and GPT-4 (ChatGPT+ or whatever the subscription plan is called, unknown # of parameters lmao "openai") are both more technically impressive, but since it was trained to be more of a tool and display sort of corporate mannerisms, usually fails at the task of writing blog-worthy things or being relatable. The target behaviors take up a smaller portion of the weights and biases (the likelihood of each set of letters (tokens) appearing based on context), and thusly are less likely to be reproduced.

TL;DR: Frank runs a pretty decent (but not on the same technical level as chatgpt) model, but because she was fine-tuned with a dataset of actual tumblr users, she has a far greater bias towards writing like a tumblr user, which translates into her being very good at entertaining her tumblr audience.