My dog threw up his Blue dog food...?

We are currently switching him to Blue Buffalo for large dogs, and he seems to otherwise be okay with it. He has been eating it for five days now, and doesn't seem to be much different than normal. He does have gas, but only as much as he always had, and it may be less stench-y now even. His waste (poop) also seems to be the same as always, but it has always seemed kind of... Odd to me. Anyway, so he threw up today, some time after eating his mix of Eukanuba and Blue Buffalo, but the only thing in the throw up is the Blue Buffalo. I found it rather strange, and a little alarming? Besides this throwing up incident, I have had no other reasons to worry. He is still as chipper as ever (even more so, as the temperature isn't so bad recently), still loves to eat all of his food and treats (though he is beginning to reject one kind, like it bores him). Should I be worried? I mean I heard that low quality foods like Eukanuba go through the system fast, which would explain why it was all gone by the time he threw up. Is this bad, or am I just losing it?