I'm not sure if they were intentionally undermining themselves so much as reacting to other things in their life that leaves them feeling a little unhappy about themself. It's common for people to do this and most have probably done it at some stage or other.
I'm not sure that person will see this post, but what they said prompted some thoughts about content and how the author and others see it, hence this post.
You said your content is beautiful and that's your opinion which you're entitled to, others may feel the same about your content also. I think mine is average, like the rest of me, although I still get enjoyment, a sense of achievement, and some personal value from the process of creating it. That's where the reward begins, and if I'm to get a favourable comment here and there that's just a little extra on top.
Thanks for your comment and all the best with your writing.