Hi,
No, the "CUSTOM FIELDS" text on the product edition page is the title of the area where all the custom fields are displayed.
And in there, each custom field has its label displayed before or on top of it.
For example, these are the labels of the custom fields on my test website :
monosnap.com/file/ZqUGpWv6wVqhwgmJE3jB4usZ5k5zh4
The fact that you don't have any text next to your WYSIWYG custom field is just because you've left empty its label as you can see on the listing of the custom fields.
And if that's not the case, then it means that the text you've added there corresponds exactly to a translation key for which the translation is empty.
For example, if I have a translation key:
FIELD=""
And then I use the text "field" as label of my custom field, the label displayed everywhere will be "" instead of "field".