Hmmm … so sometimes if Charlie is in the yard looking through the gate, someone walks past he barks, he looks round I say "thank you" he comes in for a treat - is that good?
You are rewarding Charlie for behaviours, he barks to let you know someone is there, you let him know that you've noted it and all is ok and he gets his treat because he didn't continue to bark. He's not being rewarded for nothing. It's not a bad thing for a dog to let you know someone is about. You've used a verbal cue and not a hand cue, the same as many of us. It's just different approaches.
In my book it is absolutely fine . Don't worry about it being good or bad or backward chaining I don't think it matters that he looks to you after he has barked and gets rewarded with a response and then comes in for a treat. He stops barking and doesn't just bark to get a reward. Just relax and enjoy - oh and stop worrying