Apparently an official bug, answer from Sitecore support
"A bug in the current version of Sitecore XP. To track the future status of this bug report, please use the reference number 120395. More information about public reference numbers can be found here.
These <meta> tags were added to aspx pages in Sitecore Client by mistake. Browsers ignore the X-Frame-Options header if it is sent with the document and not in HTTP header. Please note that there is an HTTP module in web.config, which adds this header to requests. Therefore, you can safely ignore the errors in browser console."