Without seeing the balance sheet, it’s hard to know whether it was bad deal. Maybe the company had a lot of liabilities. Maybe the owners already drew out a lot of the cash value of the company before the sale. As Rod noted, the residual bit isn’t something to sneeze at.
On timing, one could argue this is one of the best times to sell—right after a success. We also don’t know if the former owners are staying on (seem to be, at least initially) and what type of employment package they got. Perhaps they just wanted to trade their equity in for a certain payout rather than the volatility of ownership.