Is this hacking?

Yep, that looks like typical hacker defacement code and text. It would be impossible for me to tell you how the hack was done. You should assume the worst case scenario that you hosting account is compromised and do the steps in this link to clean up your hosting account: https://forum.ait-pro.com/forums/topic/wordpress-hacked-wordpress-hack-cleanup-wordpress-hack-repair/

Assuming all questions have been answered – the thread has been resolved.

I received your direct email to us and will answer your questions here so that this will also help anyone else who has the same questions. The defacement hack was caused by the security vulnerability in the WordPress REST API in versions 4.7 and 4.7.1. 1.5 million websites were hacked due to that WP REST API security vulnerability. The WP REST API security vulnerability was patched/fixed in WP 4.7.2. Since this was large scale hack that was done in mass/volume, then it is probably safe to assume that the extent of the hack was simply just defacement via injected text into your Posts DB table by exploiting the vulnerability in the REST API posts route: https://www.example.com/wp-json/wp/v2/posts.

So you just need to clean up your Posts and remove the injected text. I don’t believe you need to do a complete restore of your website files and database, but if you have a recent backup of files and your database then you can restore your site from that backup and then upgrade to WP 4.7.2.