Yes, you understand correctly. The minimum amount to withdraw is an amount that would cost 1000 USD to buy. When withdrawing that amount, you would get 350 USD
I'm not sure if this has been mentioned yet, but it's also important to note that not all Robux is equal. There's more information at https://en.help.roblox.com/hc/en-us/articles/115005718246 under section 3.B.
Also note that there is a comment in the video that you need to be careful how you spend your Robux for buying development, because if you are not then a cut gets taken, which maybe relates to 3B for the person you are paying?