ohhh, I see what happened. ok, let's try again, but this time with more annoying steps. it may actually be worth posting in the Q&A forum to see if MWG can update the forum software to a version that embeds x.com links (which may or may not be available yet), because this is crossing well into "hardly worth it" territory. but I'll post instructions for completeness, because me.
paste the link in your post. place the cursor anywhere in the link and tap the "link" icon in the tool bar. you'll get a popup link editor, and in that, change the URL in either field from x.com to twitter.com. select and copy the whole link you've changed, then click the "remove link" button. the entire x.com link in your post should be selected at this point, so you should be able to just delete it or paste over it or something—I don't know how iOS text editing works.