It's very hard to be specific without seeing the dog and handler together, so take this for what it's worth. That sounds like a confused dog that has endured a "butterfly" training regime and continues to do so. Not much sign either of leaving something in it for the dog, just a ratcheting up of aversives. Dogs don't get much out of heeling training so I try to be creative and give them some fun.
So I agree with Ken when he posted only I'd take it a few steps further (pun intended) and put the kibble / treat into a more formal and precise system and initially
teach heel via clicker, and develop / reinforce through repetition using a loose slip lead stopped behind the ears (as per Delmar Smith) as a safety belt and simple retrieves as a reward, plus praise.
The advantage of clicker with the sticky ones is that they don't shut down and you don't even need a lead initially so the bad reaction to it is sidestepped, and all you look for is a wee improvement in each (short) session. There's no need to look for perfection, just steadily increasing precision and body positioning. Again we haven't seen the handler, but his own body language should be regular and precise. Within a session break things up so that you don't become predictable or boring. See below .....
No heeling stick, pinch collar, e-collar or ropes were harmed in the making of this movie by Richard Biggs, professional gamekeeper and guest trainer with our group.
Eug