It is probably part of a particular way of teaching reading. I wouldn't get too excited about it.
Strictly speaking, we can never see vowels, so that "W" sitting there on the page is not a vowel and neither is this "A". We can only hear vowels. Vowels are sounds. Loosely speaking, the vowel letters A, E, I, O, and U are often called vowels. "Y" and "W" may or may not be included among the vowels, depending on the teaching method.
The typical sound we make (in English) when we see the letter "W" is called either a semi-vowel, a semi-consonant, or a glide. The same terminology can be used to describe the sound of "Y" in the word "Yes". The sound of the "Y" is a front glide related to the sound "EE" (bee) and the sound of the "W" is a back glide related to the sound "OO" (boo).
A good reason to include Y and W as vowels (vowel letters, actually) is that they pair with other vowel letters to create digraphs which have characteristic sounds. "AY", "EY", "OY", "AW", "EW", "OW". But when not at the end of a word, these are "AI", "EI", "OI", "AU", "EU", "OU". (Of course there are exceptions. That's how English is!) Because Y and I form a pair that substitute for each other, and W and U also, it's not such a bad idea to include both when introducing the concept to children.
Hope that helps!