Looks normal to me. Babies grow out of acid reflux. Just make sure to burp regularly. You'd be surprised how much they can spit up and doctors will not be concerned. As long as he's gaining weight then you're good. Its also no longer a best practice or recommended to treat reflux with medication.
Our baby is doing the same but it’s flem/mucys. Are they under the weather? X
My son is now 1 years old, this is normal and will happen on/off until they stop spitting up. Don’t know what it is but tbh it never worries me as a lot of weird stuff comes out of them lol
We had this once with our boy but out of hours didn't seem concerned about it. Just said if anything changes in terms of behavior, feeding and temperature call them back 🤷♀️ god knows why it happens (sorry, no help 🫣)