Replace your first sentence with “will you buy this car from me for $10000” and that seems like a pretty clear verbal contract.
Of course verbal contracts are tricky, but this particular case was in writing.
Just like a customer asking for a price check, a seller asking if a customer is interested are normal parts of conversations that occurs between buyers and seller before a sale is made final. Regardless if it is in writing or not, the important part is if there has been an general agreement between the two parties. That agreement is what forms a contract.
If I go to a store and point at some knickknack and ask "how much for that?", the clerk says "$1", I say "that's a deal", the clerk say "you got to be a member of the club, which cost $1000", then that is not a break of contract. Depending in the jurisdiction it could be an illegal contract or false advertisement, but those tend to take a perspective of protecting customers against being tricked. That is a harder case to make when its the seller that refuses to agree to the sale.