When you apply for financing through Tesla, they forward your application to a few of their preferred lending partners. This list includes Chase bank, US bank, TechCU and others. I believe Chase and US bank are their top preferred lending partners so they send you loan offers from these two banks first. If you're not happy with these offers, you can request them to forward your credit application to other lending partners (such as TechCU) that they work with. That's what I did. I asked them to forward my application to TechCU when I didn't like Chase bank and US bank offers.
Why it's better to ask Tesla to forward your application to a specific lender (such as TechCU) which they partner with? It's because
(a) If you apply to TechCU (or any other lender) directly, it will be seen as a separate "hard" credit check inquiry. If you apply to 5 different lenders individually, all of them will be considered separate inquiries. It may lower your credit score temporarily. I know that major credit agencies consider multiple auto loan inquiries within 1-2 weeks as "one" inquiry but all of those inquiries will be shown on your credit report for next 2 years. I didn't want this. So, I asked Tesla to work with TechCU directly. In this case, TechCU didn't pull my credit again. Instead it used the info that Tesla got when they pulled my credit first time
and, more importantly
(b) It's always easier to let Tesla work with Bank/CU directly so you don't have to worry about coordinating between two companies, extra paperwork and other things. In my case, after I said yes to TechCU offer through Tesla, Tesla is working with TechCU directly to get my loan funded. All I have to do is show up on delivery day and be ready to sign some docs. As additional "generous favor", Tesla has agreed to pay $25 membership fee that I would have to pay to TechCU if I had apply for loan on my own -
Hope this info answers your questions!