Did some more digging and this is what I’ve found.
This is ACF4, it has the code icon to edit the source, ACF5 uses the standard WP visual/text option.
I thing, though I could be wrong, that for ACF4 the icon and the code editor itself are the native TinyMCE icon and editor.
I know that bugs are still being fixed in ACF4, but I don’t think that improvements are being made at this point.
