Just because it's 'not much time for turnover' doesn't mean there's plenty of younger companies with much higher lifetime turnover.

In the tech industry, the average annual turnover rate is 13.5%. If I'm doing my math right, that amounts to a lifetime turnover of 77% for an average 10 year tech company assuming flat employee count over the time period, or 51% for the same company with linear growth from zero over the time period. Both are well above the 10% this company is claiming.

(The 77% came from 1 - ((1-0.135)*10), and the 51% came from 1.0 - ((1-0.135)*10)0.1 - ((1-0.135)*9)0.1 - ((1-0.135)*8)*0.1 ... to sample even cohorts of 10, 9, 8, etc. years making up equal portions of the population.)