(See the link you posted, the commentary explains why he was soo nice. He saw the gold that Eliezer gave to her.
. Now Rebecca had a brother whose name was Laban, and Laban ran to the man outside, to the fountain. כט. וּלְרִבְקָה אָח וּשְׁמוֹ לָבָן וַיָּרָץ לָבָן אֶל הָאִישׁ הַחוּצָה אֶל הָעָיִן:
and Laban ran: Why did he run and for what did he run? “Now it came to pass, when he saw the nose ring,” he said, “This person is rich,” and he set his eyes on the money. — [Gen. Rabbah 60:7]
וירץ: למה וירץ ועל מה רץ, ויהי כראות את הנזם, אמר עשיר הוא זה, ונתן עיניו בממון:
30. And it came to pass, when he saw the nose ring and the bracelets on his sister's hands, and when he heard the words of his sister Rebecca, saying, "So did the man speak to me, " that he came to the man, and behold, he was standing over the camels at the fountain. ל. וַיְהִי | כִּרְאֹת אֶת הַנֶּזֶם וְאֶת הַצְּמִדִים עַל יְדֵי אֲחֹתוֹ וּכְשָׁמְעוֹ אֶת דִּבְרֵי רִבְקָה אֲחֹתוֹ לֵאמֹר כֹּה דִבֶּר אֵלַי הָאִישׁ וַיָּבֹא אֶל הָאִישׁ וְהִנֵּה עֹמֵד עַל הַגְּמַלִּים עַל הָעָיִן:
over the camels: to guard them, as (above 18:
:“And he was standing over them,” in order to serve them.
על הגמלים: לשמרן, כמו (לעיל יח ח) והוא עומד עליהם, לשמשם:
31. And he said, "Come, you who are blessed of the Lord. Why should you stand outside, when I have cleared the house, and a place for the camels?"