If the vendor doesn't specify, ask. If the vendor doesn't answer, you aren't compelled to buy it.

This problem was partially created by Adobe. Judging from Rob Lister's screen captures, they format is being indicated correctly. ePub is ePub and PDF has been referred to as Adobe in many circles ever since Adobe dropped the Acrobat.

PDF is a perfectly acceptable ebook format. The fact that it's a page description language doesn't exclude it from that categorization, it simply makes PDF harder to use on different screen sizes and aspect ratios. Yet it has been utilized for purely electronic documents for years.