It's almost certainly A/B test. Essentially everyone does it.
You can even sometimes see when a list of videos on YT first loads and a given video has one title, and it suddenly switches to another without you reloading the page.
On several channels I watch, I've noticed the top comment is always along the lines of "who was here when the video title was XYZ" because you know it's going to change.
Either they changed it for some legal reason, or Youtube allows for A/B testing of multiple titles for engagement.
You can even sometimes see when a list of videos on YT first loads and a given video has one title, and it suddenly switches to another without you reloading the page.