Where are facebook style link previews populated from?

Hi! I have just built a page with vantage, it has been wonderful to work with. I noticed that when I a link to my page on FB, the preview reads “Under Construction!” and I have no idea where that text is coming from. Any idea?

I know that my subheading reads “under construction, please hold”, but that is clearly not the same text.

page preview on fb

the homepage

Thanks,
Brandy