If this set includes all 102 cards in the first BASE SET and they are all shadowless / 1st edition / PSA10 Graded then I am honestly not surprised. As these cards get older there will be fewer and fewer left at this quality as well.
The kids growing up with these cards are now to a point where they want their old set back for nostalgia. They now have good jobs and some (like this guy) are very well off. If he is rich he will buy the best because why not, and this set would be the best if they are all original shadowless 1st edition psa10 cards. Lucky guy.
For comparison, I bought the complete shadowless / 1st edition base set cards, 1st ed jungle set cards, and 1st ed fossil cards to get me the original 151 and also bought the next 1st ed neo sets to get me the original 251. This was 4/5 years ago and they were not PSA graded cards, but still cost me like $2,000 total. The 1st edition shadowless charizard card is always the most expensive one to buy. That alone cost me $500 back in the day and I believe goes for $2k or $3k now a days.