The reason tariffs are not inflationary is that the goods which face increased costs and are sold at a higher price, that is a direct source of increased demand for money. If these firms and those affected by no longer spending at them have additional money to spend elsewhere, that is an increase in the supply of money for other goods, and it is unlikely to surpass the effect of the increased demand for money elsewhere. The other thing is that tariffs make planning difficult, which in a more general way across the economy and especially in production, increases the demand for money and lowers its supply (money being a way people handle uncertainty).

So really tariffs artificially shift around economy and increase costs, but do not cause any significant inflation on their own. This narrative of causing inflation comes from a lack of understanding of money and propaganda to control the narrative and diffuse blame for monetary debasement.