That's nonsense. Booking.com with it's subsidiaries was about 18000 or so people when I left in 2017. About 1800 of that were in engineering The vast majority of staff were working either on the supply or customer service side.

According to Google Finance:

BKNG: Employees: 23,100, Revenue(2022): 17.1B, Net Income(2022): 3.1B

ABNB: Employees: 6,811, Revenue(2022): 8.4B, Net Income(2022): 1.9B

https://www.google.com/finance/quote/BKNG:NASDAQ

https://www.google.com/finance/quote/ABNB:NASDAQ

I don't know about booking.com, but when Facebook acquired Instagram for $1B they only had 13 employees. WhatsApp had 55 employees when they were bought (again by Facebook) for $19B.

Crunchbase says it's closer to 10000.