Wow, the Bible says that the Israelites weren't faithful, and the evidence points to that. Who could have guessed? No, this is not evidence of Polytheism.

Elohim can be used as a title, and used with singular verbs, especially when it refers to Yahweh. Angels are Elohim too, it's basically just their word for spirit or any supernatural entity, not exactly just gods. Even dead humans are called Elohim.
And yes, Israel did turn to pagan worship, there's entire sections of the Bible talking about it, but the key difference is that it's not their original or main god; The Bible makes a point that Yahweh is the God of their ancestors, and archaeology points to the Israelite practicing Yahweh worship for quite a while.