Url thumbnail not displaying image

Hi, I have a question, why when I try to use url_thumbnail in the <img src={url_thumbnail}/> does the alt text of the image display? The link in src is correct and when I paste it into the browser, the image downloads, the problem is only when I try to display it as image using <img/>. I noticed that the same behavior occurs for the url field, only when I use public_url the image displays. In that case, what is this url_thumbnail for if I can’t use it to display? This is my query:

query getFiles($boardsIds: [ID!]!) {
  complexity {
    query
  }
  boards(ids: $boardsIds) {
    id
    name
    items_page(limit: 500) {
      items {
        id
        name
        column_values {
          __typename
            ... on DocValue {
        file {
          file_id
          url
          doc {
            url
            name
          }
        }
      }
          ... on FileValue {
            value
            files {
              __typename
              ... on FileAssetValue {
                asset {
                  id
                  name
                  url
                  url_thumbnail
                  file_extension
                  public_url
                }
              }
              ... on FileDocValue {
                file_id
                doc {
                  name
                  url
                }
                url
              }
              ... on FileLinkValue {
                file_id
                name
                kind
                url
              }
            }
          }
        }
      }
    }
  }
}