Was scrolling through yt videos and then i saw this motivating video, but it had like an image of a girl with her huge ass almost exposed as the thumbnail. I kinda scrolled away as fast as i could. Is this a relapse?
That's part of the reason why I quit YouTube all together (the other reason being it's too time wasting, similar to basically all other social media). I consider a relapse only if you're consciously and deliberately doing PMO. I might consider this case as a reset, but not a full relapse.
The image you describe is not porn. Porn is a depiction of people in sexual activity, and just having a huge ass is not sexual activity. So unless you fantasize to it and start masturbating, everything is fine. Take a deep breath and relax.