The first part of this is correct, by default we block loading of Discourse sites in iframes. It protects your site from a variety of risks, from SEO tricks to clickjacking (see this for more details).
The second part is odd though, webviews are definitely not iframes. Webviews are mini-browsers that can be embedded in mobile apps, they act like a real browser. An iframe is a way to load one webpage inside another webpage. I guess the whole Glide app is essentially a webpage, so they’re using iframes inside the webview there, maybe?
We have a site setting that can be toggled to allow your site to be embedded in an iframe, but we don’t recommend doing this, and there are quirks with Discourse inside an iframe. In other words, we can enable iframe embedding for you, but there might be unfixable problems down the road.