What does なんだろうけどな mean here?

Question

「ムラサメ様のことを疑っているわけではなくて、慣れない生活ですから、体調を崩すこともあると思っただけです」」

「何もないならいいんです。それでは失礼します」

「あ、はい」

「いい子、なんだろうけどなぁ。俺を心配してくれてるんだから」

What does the なんだろうけどな mean in the above exchange?

I think I understand what he means (despite her acting cold and trying to distance herself from him, he suspects that she is actually a nice girl, evidenced by her worrying about him). However, I'm still not quite sure why the けど is there. Without the けど it wouldn't make sense/sound right, but I can't quite put my finger on what its doing.

1. Is there something after the けど that is left unsaid?

2. Is it backwards so that the kedo comes at the end of the second sentence? (I.e. there is something that previously happened or was said, like in the question Understanding この場合〜なんだろうけど?)

3. Something else?

Answer 1

As you have correctly guessed, "俺を心配してくれてるんだから" is the reason why he thought "(彼女は)いい子なんだろう". So the normal word order is like this:

俺を心配してくれてるんだから、いい子なんだろうけどなぁ。

This sentence-end けど implies the speaker does not unconditionally agree what he has just said. Perhaps he could have continued by pointing out her fault, for example, like 「（俺を心配してくれてるんだからいい子なんだろうけど、）やっぱり外見はとても冷たく見えるよな」 or 「（いい子なんだろうけど）まったく笑ってくれないのは残念だなぁ」. In this situation, what he wanted to imply by saying けど was rather obvious from the context. But that's not always the case. One might say けど when even he is not aware of what he wanted to say after けど.

Reference:

• けど at the end of the sentence?
• What does んだけど mean here?