Rich Text Area fields are stored in HTML, where characters such as apostrophes are escaped. That is what you're seeing here. It's behaving as designed and cannot be changed.
From Editing Rich Text Area Fields in Records:
Rich text field values are returned in HTML format. Some characters are escaped when the custom field value is retrieved through the API.
- Ampersand character & is returned as
&.- Greater than character > is returned as
>- Less than character < is returned as
<- Quote character " is returned as
"- Single quote character ' is returned as
'
