By looking at the source code for Mudcat's web pages, it doesn't appear that the text size it set by the HTML code. If that's true, then the text size you see is controlled by your browser's default setting.

Do you see giant-sized text every time you go to Mudcat, or did this happen only once? If it's happened only once, it could have been caused by a loading problem - maybe the page got mangled by line noise while it downloaded. Or, if it happened only once, maybe the text size got set too big by the site you visited before Mudcat. If it happens every time, then I'm sorry, but I don't know what might be causing it.