Translation:This dress is a little bit short.
No. 1) When you want to say something is a little bit too something (often in the negative way) you always use 有点儿/有点, and BEFORE the adjective. For example : 这件外衣有点儿大 This coat is a little too big! (negative). 2) When you want to say something is a little bit more of something positive you use 一点/一点儿 AFTER the adjective. For example: 今天我觉得好一点儿了 I am a little bit better today.
3) When talking about a NOUN, and you want to say a bit of something, you use 一点/一点儿 before the noun. For example: 我想喝一点儿东西 I want to drink a little bit
If you ask me, it doesn’t make a difference if you say 有点儿+Adj or 有一点儿+Adj, except maybe in terms of emphasis (if unemphasised I would pretty much invariably leave out the 一). Both carry the slightly negative connotation you are talking about: “This skirt is a little bit [too] short.”
Note that the video also doesn’t contrast 有点儿 and 有一点儿 (in fact, it doesn’t mention 有一点儿 at all, except as a combination of the verb 有 “to exist” + 一点儿). The contrast it does point out is between Adj+(一)点儿 “a bit more Adj” vs 有点儿+Adj “a bit too Adj”.
the difference between 一点儿 and 有点儿
一点儿 is a quantifier, used to refer to a very small amount or low degree:
请给我一点儿盐。Please give me a bit of salt. 我能说一点儿英语。I can speak a bit of English.
我想要个大一点儿的电视。I want a bigger TV.
all "一" in the sentences above can be omitted.
有点儿 is an adverb, is used to refer to a very small amount or low degree. It is often used to describe something unsatisfied, abnormal or to show discontent:
我有点儿累了。I am a bit tired.
弟弟有点儿不高兴。The (younger) brother is a bit angry.
地板有点儿脏。The floor is a bit dirty.
We sometimes hear or see 有一点儿 too, let me talk about it a little bit:
有一点儿 sometimes just equals to the adverb 有点儿, but it's slightly different: 我有点儿累(You generally tell people you start to feel the tiredness) = 我有一点儿累(You tell people you are a bit tired not very tired). The two expressions stress different facts. The difference is very tiny and subtle, you don't need to worry about it.
Besides, 有一点儿 can mean something very different from what we have above, it's a combination of the verb 有 and the quantifier 一点儿, so the phrase is 有+一点儿+n.
我们有一点儿钱。We have a bit of money.
外面很黑，但有一点儿光。It is very dark outside, but there is a little light.
一 in these sentences can also be omitted as we do with 一 in sentences with "一点儿".