This year when I planted my bush green beans I also had pole beans mixed in. When I questioned the seed company about why they sent me pole beans mixed in with my bush, they said that when bush beans get stressed they revert back to pole beans because that's what they actually come from. I don't believe that's true, is it?
This is accurate. Proper care will ensure that they do not get stressed and revert. This article will help you with their care:
https://www.gardeningknowhow.com/edible/vegetables/beans/growing-bush-beans.htm
First time planting a veggie garden alone. Hubby has lots of advice but I want to know why I should thin.
It's always best to thin out seedlings to prevent the competition for nutrients and water. It also increases air circulation. Plants too close together are more susceptible to fungal infections due to lack of air movement.
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/thinning-seedlings.htm
https://www.gardeningknowhow.com/edible/vegetables/beans/growing-bush-beans.htm
I built several different sized planter boxes that have legs so they're different than the typical raised planter box. The planter box I want to use is about 2 ft by 1 ft.
Bush beans get about 1 foot wide so you have room for two plants.
https://www.gardeningknowhow.com/edible/vegetables/beans/growing-bush-beans.htm
This started on the right side of my planter and is spreading to the left
This reminds me of the fungal bean rust. Here is an article for treating such infections:
https://www.gardeningknowhow.com/edible/vegetables/beans/rust-fungus-on-beans.htm