覗かせている meaning in this sentence

Question

入学当初よりも学力を伸ばし、そして精神面での成長も覗かせている須藤は、2年次から記録されていく成績を大きく伸ばすことになりそうだ。

I'm a bit confused with the meaning of 「覗かせている」 in this sentence.

覗く: jisho.org

1. to peek (through a keyhole, gap, etc.)​,

2. to look down into (a ravine, etc.),

3. to peek into (a shop, bookstore, etc.)​,

4. to sneak a look at; to take a quick look at,

5. to peep (through a telescope, microscope, etc.)​,

6. to stick out (a scarf from a collar, etc.); to peek through (sky through a forest canopy, etc.)​,

7. to examine (an expression); to study (a face)​,

8. to face​Archaism.

Based on the structure of the sentence, I have a feeling that the word 「覗かせている」 means the subject (須藤) shows his growth, rather than other people see his growth.

Please kindly give me your guidance, thank you.

Answer 1

You're right that the subject (須藤) shows his growth.

Here, the subject of the causative verb のぞかせる is 須藤. And the object of のぞかせる is 精神面での成長. So the subject/agent of のぞく "peep out" is 精神面での成長.

［精神面での成長も覗かせている］須藤
(≂ 精神面での成長も見せている須藤)

⇒ 須藤が(=subject) 精神面での成長を(=object) 覗かせている (causative "make something peep out") (も has replaced を in your example)
"Sudo makes his growth peep out" → "Sudo shows his growth"

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Some examples of this のぞかせる, "make something peep out", i.e. "show", from プログレッシブ和英辞典:

• 胸のポケットから折り畳んだハンカチをのぞかせて、カメラの前に立った。
  He faced the camera with a folded handkerchief peeping out of his breast pocket.
  (Literally: (He) made a folded handkerchief peep out of (his) breast pocket, ...)
• 太陽が雲間から顔をのぞかせた。
  The sun peeped [peeked] out between the clouds.
  (Literally: The sun made its face peep out... → The sun showed its face...)