I'm not defending Tesla, but rather pointing out that when you get a trade-in quote from Tesla, they always expire after 30 days and it is clearly stated in plain language.
Now, in this case you're right - there was a subsequent signed and paid-in-full MVPA, which is the final contract. Complicating things is the way Texas does things (er, how Tesla must do business in Texas due to arcane dealer-protection laws) where Texans must pay in full before the car is in the buyer's possession. I agree in this particular case that the poster has a valid claim for breach of contract.
For the others here that complain about Tesla not honoring the quotes after 30 days, I'm not so sympathetic, unless they have an executed MVPA with the trade-in amount as a line-item. I doubt that's the case for most.
When I first put my MY order in around the beginning of February, I got a trade in quote for our '15 MS 70D. Of course, then the COVID-19 pandemic pretty much stalled production starting in mid-March. So I knew that my trade in quote from February had expired. In late April, in anticipation of the factory re-opening, I once again asked for a trade-in quote, which was within $500 of the first offer but expired in 30 days (by late May).
I then sold the MS on eBay in early June for more than what Tesla had last quoted. Why? Because I expected any new quote to be markedly lower than the February and April quotes. I knew it was on me to either sell it privately or get another trade-in quote within 30 days of getting the MY. I'm not sure why people assume that a document that clearly expires in x days isn't honored and are upset by that fact.