Blown head gasket?

I recently had a lot of engine overheating due to a failing water pump, a dirty radiator and a sticking thermostat. I had a mechanic flush out the radiator then replace the water pump and the thermostat. They only added about 3 1/2 gallons of antifreeze it’s I’m assuming the other 3 1/2 gallons, my truck holds about 7 gallons, was left in the engine block. They also added a new overflow bottle and then fill up the vehicle with new coolant, 3 1/2 gallons. My vehicle was overheating a little bit after that because the thermostat was sticking but now it has been running fine and I have drove it about 1000 miles since then and I’ve only had the thermostat stick just a few few times but it seems to be working normally if you let idle at a cold start up to operating temperature then the thermostat works like it should. My problem is, there is still garbage in the overflow and wondering if it was that old dirty antifreeze that was left in the block that’s mixed with the new. I did have gone under my overflow cap, but it wasn’t like a milkshake. It was a little wet but mostly dry. There is nothing in the oil as the oil is clean and underneath the oil cap there is no gunk either. Do you think I have a blown head gasket or do you think oil is mixing in somehow causing the coolant to be dirty even though there is no coolant in the oil, possibly a bad oil cooler, or do you think that the garbage that was left in the engine block mixed with the new coolant and that is why the overflow has gunk in it? Do you think it’s a blown head gasket even though the bucket truck is driving fine?