jeogi usgo issneun geol boni geu sosigi jeongmal bangawossna bwa.

No. In this sentence, 저기 means over there. It points to someone or something at a distance from the speaker and listener.

So 저기 웃고 있는 걸 suggests something like that person over there smiling or the fact that they’re smiling over there.

Korean often leaves out a noun like 사람, so 저기 can feel like that person over there even when 사람 is not actually said.

It comes from:

• 웃다 = to smile, laugh
• -고 있다 = be doing
• 웃고 있는 = smiling / laughing

Here, 웃고 있는 is in the form that modifies a noun. The noun is not stated directly, but it connects to 것 in 걸.

So 웃고 있는 걸 is literally the thing/fact of someone smiling, and more naturally someone smiling or the sight of someone smiling.

걸 is a contraction of 것을.

• 것을 → fuller form
• 걸 → common spoken contraction

So:

• 웃고 있는 것을 보니
• 웃고 있는 걸 보니

mean the same thing. The version with 걸 sounds more natural in everyday speech.

Literally, it is something like seeing the fact that someone is smiling.

More natural English meanings are:

• seeing that they’re smiling
• judging from the way they’re smiling
• from seeing them smile

The pattern -는 걸 보니 is often used when the speaker observes something and makes a conclusion based on that evidence.

보니 comes from 보다 + -니.

In this kind of sentence, -니 often gives a sense of when I see/after seeing, I realize or judging from what I see.

So 웃고 있는 걸 보니 is not just I saw them smiling. It means seeing them smiling, I can tell that... or judging from that, ....

It introduces the speaker’s inference.

Because Korean often omits subjects when they are clear from context.

In this sentence, the person who is smiling is understood from 저기, and that same person is also understood to be the one who felt glad about the news.

English usually has to supply a subject like they, he, or she, but Korean does not need to say it if the listener can figure it out.

Yes, grammatically 그 소식이 is the subject of 반가웠다.

With 반갑다, Korean often treats the thing that someone is glad to hear/see/receive as the subject:

• 그 소식이 반갑다 = literally that news is welcome
• natural English = someone is glad about that news

So Korean frames it a little differently from English. English focuses on the person’s feeling; Korean often focuses on the thing that was welcome or pleasing.

반갑다 does not just mean general happy. It has a more specific nuance:

• glad
• pleased
• happy to see/hear/receive something

So 그 소식이 반가웠다 means the news was welcome or pleasing to hear.

That is why it fits very naturally with 소식.

-나 봐 expresses inference: the speaker is guessing or concluding something from evidence.

So 반가웠나 봐 means:

• it seems they were glad
• I guess they were really glad
• they must have been glad

It is not a direct statement of known fact. The speaker is inferring the feeling from the visible clue: the person is smiling.

The past tense sounds natural because the speaker is talking about the person’s reaction to the news—how they felt when they heard it.

So even if the person is smiling now, the sentence is interpreting that smile as evidence of a reaction that already happened:

• that news must have been really welcome to them
• they must have been really glad to hear that news

If you used a present form such as 반가운가 봐, it would focus more on their current state of being glad. The past form is very common and natural for this kind of inferred reaction.

Yes, but the nuance changes a little.

• 반가웠나 봐 = the speaker is inferring the person’s inner feeling
• 반가워했나 봐 = the speaker is talking more about the person’s outward behavior, as in they seemed to be acting glad

So 반가워했나 봐 can sound a bit more observational, while 반가웠나 봐 sounds like a conclusion about what they actually felt.

Both are possible, but the original sentence sounds very natural in conversation.