Smart people do not default to thinking that others are stupid.
They go through the answer space, exhausting the other options and then settle on "that guy must be an idiot" with a confidence level somewhere in the high 90%.
It has to be this way, because stupid people do in fact exist. So there must be a process of which the outcome is thinking that someone might be stupid.
And smart people suffer [0] [1] [2] [3] [4] exactly because they, first, think that others can have the same scrutiny about things and get surprised/disappointed when they find out how other people reach conclusions. Loneliness is the most common.
[0] https://doi.org/10.1111/j.0963-7214.2005.00328.x
[1] https://doi.org/10.1111/bjop.12181
[2] https://doi.org/10.1016/j.intell.2020.101465
[3] https://studenttheses.uu.nl/handle/20.500.12932/28009
[4] https://link.springer.com/article/10.1007/s43076-023-00313-8