The code in itself is not an HTML5 advert nor does it use an iFrame.
This is just an ordinary image advert. Except the image is missing too. And the link bit is kinda wrong.
Try this instead: <a href="URL_GOES_HERE" target="_blank"><img src="%asset%" /></a>
Obviously replace URL_GOES_HERE with your target url, the site where people end up when they click the advert.
And a little below the AdCode field you can upload your banner image to the media manager – That’s what %asset% translates to.
The %asset% is a link to the .html file for an html5 banner, not an image
When I use the code you provided above I get no image presented at all. (Broken square placeholder)
When I use the iframe code the image appears but is unclickable
Here is the actual code with the link and source in longform: