An ad may not appear correctly on mobile phones if it:
- is in Lightbox format
- uses HTML5
- isn’t optimized for mobile
- uses Flash or contains large images
An ad may not appear correctly on mobile phones if it
Using Flash or large images could create rendering issues on mobiles. But that also means that it’s not optimized for mobiles. I don’s see personally a differences between 2 answers, both seems equally correct. Probably “isn’t optimized for mobiles” refers more to landing pages or you site, not to an Ad.
To make sure your ad looks great on the small screen, you can create a mobile-optimized ad with a message, display URL, and landing page specifically for mobile devices. To do so, select the “Mobile” checkbox next to the “Device preference” setting. If your ad groups contain ads that are eligible to appear on all devices and mobile-optimized ads, only your mobile preferred ads will appear on mobile devices.
You can read more here: https://support.google.com/adwords/answer/2472719?hl=en