If he'd been thinking quickly, he would've spoken up before Tonks' 'introduction' and would've apologized for interrupting, but said that he was in for a check-up on his shoulder and that they hadn't told him that Andromeda was in with her daughter, just that she was in this room. But, it was too late to give that excuse now, clearly, so Bill simply hovered close to the door instead of going to the other side of her bed like he wanted to do, in case he needed to make a quick exit.
Andromeda's tone of voice surprised him, they were generally on good terms with one another. Though, it most certainly reminded him of one his mum used - the whole mother bear protecting her cub sort of thing - so he wasn't entirely taken aback by it. The story that went through Tonks' mind also came to Bill, but he figured lying to Andromeda wouldn't win him any points either, because she would eventually find out that they were together, whether it was today or months on down the line. Not that it would have been entirely a lie, either, as they had a glass or two of wine with dinner and she had crashed at his place, just not on the couch.
With both Tonks and Andromeda's eyes on him, Bill's face flushed, one of the few times in his life that he'd been truly embarrassed by a situation. Finally, he spoke, gesturing to Tonks with one hand, "She's uh right...I brought her in. She was out cold. Brought her here not only because of that, but because I was worried she might have a concussion." Maybe showing Andromeda that he'd been trying to be responsible and take care of her daughter would help just as much as Tonks talking it up a bit.
He couldn't tell if that was a hint from Tonks for him to leave while he was still capable of walking out of the room or not, but he wasn't going anywhere...unless Andromeda asked him to leave or made him, of course. Shaking his head, he said, "I am, but making sure you were alright was more important. There hasn't been a whole lot of treasure coming into the bank the past week anyway, so I'll catch back up on my work quickly enough. Are you alright? What did they say?" He'd been looking back and forth between the pair of them, but his gaze settled and focused on Tonks at his questions there at the end.