Got a strange one hadn't seen before.

Rows show as 1,2,3,
but columns showing as 1, 2, 3.... not A, B, C, D

Can't figure out how to out back as A, B, C, D.....

How does that happen, is this a feature where you can change it, if so how?
Good to know for future references, and if did change how to change it back.

Thanks