1. While mobile video viewing is definitely booming, remember that many of the numbers you see also include at-home viewing over the home WiFi network. Which is very different than out-of-home viewing over an LTE network. (And the stats are rarely split to show the difference between the two.)
2. The reason more people watch video on their smartphones than on their tablets is that more people have smartphones than tablets. So raw number-wise, the smartphones are always going to come out on top.
Stats are great and all, but it's always important to maintain a degree of skepticism as to how they were collected. Self-reporting in particular always troubles me, as people tend to self-report the behavior they want to have, not the behavior the actually have.