Oh, he sounds exactly like Ivy. Apparently, this behavior isn't all too uncommon, but it doesn't fall under a singular umbrella term like "aggression" or anything. It's pretty subjective and open to interpretation, but from what I gather and understand is this:
- These dogs are easily aroused/overexcited. They don't have coping skills to deal with the influx of emotion and adrenaline and so take their frustration out through lunging/biting. They are often dog-friendly off leash and rarely, if ever, get in fights off leash. These dogs generally have very very low thresholds.

Because their thresholds are so low and because they don't know how to deal with themselves, we have to teach them. It sounds strict, but you have to lay down the rules from here on out:
1) Enforce NILIF now to bring a solid structure and foundation into the household. Teach "Wait" and teach Taz to reorient back to you after waiting. For example, before you exit the door, have Taz wait. Release him from "wait" with a verbal "okay!", and stand there. Wait until he voluntarily looks back at you. ONLY then will you move forward. Practice this at the door, at the car, at the garden gate, at a store, etc.
2) Teach coping skills: For him, meeting a dog for longer than a few seconds is too much. He just can't emotionally cope with that so he lunges. Instead, turn meetings into positive training sessions. Taz meets dog. Click. Taz returns to you for the treat. Let Taz meet dog again. Click. Taz returns for the treat. Let Taz meet dog again. Click/treat. Repeat. Repeat until Taz views the other dog as a signal to begin this game of meeting and click/treating. Thus, in one game, you teach him to voluntarily meet the other dog and then reorient back to you. The stress of a prolonged greeting melts away!
3) Manage situations better: The owner's body language is CRUCIAL with dogs like Taz. They are often highly sensitive to the environment and to their owners. If you feel Taz getting tense and you make a slight movement, that slight tug on the leash or that slight movement of your hand can set Taz off. Rather, what you want to do is pay more attention to how you control yourself. You do want to be a strong, confident leader. You should be able to diffuse tense situations, not urge them on. So when you see Taz getting into the "red zone" and you see him tensing up, remove yourself and recall him. If you ever find him in your lap and he's getting tense, pick him up and place him in a low-stress environment (i.e. crate). You want to make sure that Taz NEVER gets above this threshold ever again. If he ever lunges from here on out, it is up to you to figure out what his body was saying to you, what you misread, and how you can prevent it. His body is speaking constantly. We just have to learn how to read them better and how to respond more effectively

Hope that helps! If you need visuals of anything I wrote (like the 'wait and reorient') just let me know!