I know that similar to Any Number, Lucky Seven usually has a ding instead of a buzzer sound effect for a loss, but I guess that a buzzer could've been used given the wipeout here. I think the show used the foghorn in Season 21 when Lucky Seven was lost on the first number. It might have been the second number for a five digit car. I believe they used the buzzer for a piggy bank win around that time. Just once, not all the time.
I really didn't have a problem here. The price of the Jeep did begin with a 9 so he was doomed. However, the show was still offering automobiles where the first digit was a 6. To be fair, if there was a $6,000 vehicle offered, and a contestant guessed 1 as the first digit, he or she would still be in the game & have a chance. Not that Bob was obligated to stop him, but he had several reasons not to, in my opinion.
While on the subject of Lucky Seven and the "historic moment", there sure have been several cases of the last digit being a one. I believe the contestants that have lost on the last number guessed 5 and had four dollars left, but ended up getting unlucky. Talk about brutal times ten! I think I might have some sympathy for another Lucky Seven contestant from the other historic moment later on this season.