Actually when you use R functions to import CSV files, they also guess data types and make some conversions by default. The difference is that in R you can turn them off if you want to. But in Excel there are automatic changes you can't turn off.
The problem with "things that look like dates being interpreted as dates" comes from not specifying that a column has type "text".
Happened to me multiple times, even when i set each cell as a text.
Seems like copypasting a tab separated values resets the cells to their default state.
Just want to know to avoid future gotchas.