If your focus (highlight) was on the Header line, Text is the only option because it is asking you to enter names (text) for each column.
It seems that 'Cell Type:' 'Field' is not available, only 'Text'.
The next line down (Row 1) when highlighted, makes the Field option available and a dropdown arrow beside the <select field> block offers an alphabetical list of all possibilities. Each Row block under each Column can contain different fields as chosen from the <select field> block dropdowns. The options icons can be clicked to insert more Rows, Columns and align the data within them. Play with that and you'll get the hang of it