Regurgitating or Vomiting

I know there are a lot of posts on this topic, I've read a few of them but I'm still not quite sure about my budgies behavior.

I own two male budgies since September, they were born this summer.

A few weeks ago one of them (Garrus) spit out some seed a few moments after I let them out of their cage and flying to their favourite perch. There was head bobbing and shaking involved, which resulted in very dry intact seed being sprayed all over the place (no clusters). He did it a few times within a few minutes then stopped for the day. The next day I let them out the same thing happened so I took him to a vet.

She said he looked healthy but flushed his crop with saline solution (?). They also tested his stool which showed some kind of bacteria. I treated both of my budgies with antibiotics and after another stool test the vet could see that the meds worked.

So yesterday and today it happened again - I let the budgies out, they flew to their perch and Garrus starts spitting seed for a minute or two. Today, when the other budgie noticed that Garrus was spitting seed he tried to get fed by him - with success a few times but a lot of seed still ended up all over the place.

Does that sound like regurgitating or do I need to visit the vet again? He shows no other signs of sickness - he eats normally, is energetic and interacts normally with his buddy Griff and me.