Comment in an Excel cell, but not a comment or a note.

Hi,

I have come across an Excel file that has a comment in the cell, however it is not a 'comment' or a 'note' (after clicking the right mouse bottom). Please see attachment for an example.

Can anybody help me, how to delete comments like this? And also, how can I add a comment like this?
Again, this is not findable on a comment or note. If I add a note, it is added separately to the cell and looks different.

Thank you for your help/thoughts/feedback!