Ok So don't like the guy but on the subject of God being Jesus I agree I don't believe they are one person. I believe they are two different people. So him thanking God and Jesus seems normal.
Sorry to start on this religious debate but being a Sunday school teacher this is one of the debates I deal with a lot.
But the entire basis of the joke is erroneous bases on his, and many others beliefs. Its like saying that Barack Obama and Malia Obama are the same person. Or Prince Charles and Prince William.
People will find any insult just to target someone, even if it doesn't make sense. Especially Tumblr VS Bieber. I don't even like Bieber, but I know (according to my religion) that what he was saying was right.
Shema yisrael Adonai elohanu Adonai echad Baruch Shem ka'vod mail choo Tay la'olam va'ed. I definitely misspelled it, but this is something along the lines of hail Israel the Lord our God God is one. I have a ring with this written on it in Hebrew. Yeshua and Yehova (not sure if I got the names right) are one entity. Aka Jesus and God. This is what the Bible says.
They are both one but also seperate. The Trinity is 3 beings, seperate but still one, a tree with one trunk but three great limbs branching out separately.
Sorry to start on this religious debate but being a Sunday school teacher this is one of the debates I deal with a lot.