Hmm.. tricky question. But I consider nearly all of them as texts. They can have different sources though. The footer details can be OTR, SO10 or hard coded texts for instance (and there are several other possibilities).
In your example, the column headings would be translated via the form per transaction SE63 ( but you might also consider to get the label from DDIC). The fixed footer I would set up (and translate) as either an SO10- (or OTR-) text (that way they can be maintained without having to change the form, and there is the re-use possibility in other forms).
Bottom line, a header of a column is can of course be described a label, but in the end it remains a text in the form 
I've seen forms where all texts and labels are maintained (&translated) in tables, SO10 texts and no texts at all in the form. Which works perfectly well (but it tends to make the form 'unreadable' as a developer if you want to know what happens where in the event you have to make some changes later on).
Anyway, if I can re-use a text (whatever it may be) in several other forms then I consider creating it outside the form. Else I keep it in the form. But that is my logic, and there are probably a lot of people that have different standards.