Well here is an article that explains a lil bit of both... FST7 is a new training principle from Hany Rambod so you can take it any way you like it. It's a routine based on ppl who like high volume training.. He also explains about the "pump"... I read up on FST7 and gave it a shot and have been doing it for a year now and has seen great improvements.. Sometimes it's ok to go outside the box and try something new. You never know unless you try it out and not be ignorant
Pumps do not mean a thing to growth. To borrow from a friend on the topic (Zir):
"The pump is due to increased pressure in the vessels forcing fluid out into the interstitial space (the area outside of the muscle cells and blood vessels). As a result of this high pressure, some capillaries may actually be compressed and a lack of blood flow will be delivered. In addition, the high pressure reduces nutrient exchange and waste product removal. Which, in terms of signalling hypertrophy, is not an overall bad thing (see KATSU training). The pump, can however, reduce recovery due to fluid not reentering the system and a build up of inflammatory chemicals, which is one of the main reasons for performing a warm down and even cryotherapy (icing, ice baths, contrast showers, etc.) post workout."
Another thing to consider is this: in order to send more blood to one area, you have to reduce the amount in another and it's usually from the digestive tract. This results not only in the aforementioned scenario, but in also slowing down the digestive process and delivering nutrients.