The media likes to make these kinds of connections between big-name historical figures and archaeological discoveries, but the truth is, there's too little evidence to give an informed answer to the question. Yes, it could be Penda. Or it could be some other guy whose name didn't make it into Bede or the Anglo-Saxon Chronicle. There were a lot of people alive in the seventh century, and sadly few of their names are recorded.

In the end, trying to figure out the name of the person or persons who buried it is just a guessing game, and not as interesting as the kinds of questions that can be answered by looking at the artifacts themselves and letting them tell us their story (instead of trying to force them into the story told by the limited written sources). The impurities in the metal they're made from, the way in which the objects were dismantled, the types of objects assembled together, the traces of decomposed organic material left on the objects - these sorts of things will tell us a lot about the objects' histories, even though we'll probably never be able to say with certainty the name of the person who buried them. And that will add significantly to our knowledge about the practices and maybe even the beliefs of the time.

I like the offering theory, but I'd urge caution in assuming the Christian images on the objects mean they were stolen and buried by pagans. We don't know a lot about religion in England during this period, and it's difficult to say that Christians wouldn't have done something like this themselves, or that the Christian symbols mean the objects belonged to Christians (who's to say pagans can't have things with crosses on them, or didn't get gifts from Christians, or didn't worship Christ alongside other deities?). Early medieval politics and religion were complicated, and rarely boil down to a simple pagans vs. Christians animosity. It was probably much more complex and interesting!