The agent at check-in would have been employed by a third party handling agent rather than by QR. Assuming that your father didn't make a point of either taking this up with the station manager (who would be a QR employee) or calling QR in Doha at the time, the fear of letting someone pass with even a minor typo in their paperwork may reflect the culture of the handling company in that location.

If you have written confirmation from Qatari Immigration that the typo in your father's father's name is not important (I think that's what you are saying, even though you missed it when checking the documentation?), you should contact QR in Doha to discuss this. You may have a case for incorrectly being denied boarding by the third party that they may wish to put right. Presumably there may be at least a partial refund due.

Make a calm case, stick to the facts, and see what they will do. You may find that they are good on the ground if you try to work with them rather than criticise them. Good luck!