Very difficult to answer this with specificity, but in general there are a number of factors that influence the amount of cash you ultimately net from a sale, including:
- Cap table: what % is owed to other founders, investors, employees, etc?
- The total acquisition price may include substantial legal and other fees that will lower the actual amount received by the owners or shareholders.
- How much of the acquisition is financed through cash vs. equity? Equity may vest over a certain time period, and be subject to certain requirements (your sustained performance, ability to clear legal scrutiny, etc.).
- Taxes.
Taking all of this (and probably more) into consideration, it doesn't seem unreasonable for a founder to ultimately net <10% of the total sale price. Again, this is all wild speculation in this particular case.