The solution is to select French or Finnish language when importing csv. Estonian and English display numbers in the preview window but fail to dates once OK is pressed. We need to use F-counterparts of the languages, Finnish for Estonian or French for English to accomplish the import properly. I am still would be happy if sombody will inform the World how to ban the Date type in the spreadsheets forever, likewise you get rid of Caps Lock.
Normally, importing CSV with English(USA) locale does recognize dot as decimal separator. But, in my case, you first imported CSV with Est locale. This formats the numbers in the spreadsheet improperly, as Dates. You select all cells, go to Cells > Formatting and choose Number with English locale, hoping to fix the problem. But, it makes things worse. This will only reformat the dates in English manner. But, if you import same CSV with English Locale, it will keep the numbers as dates. Importing French or Finnish locale, breaks the fixation and you get the numbers finally.