Translation:This dress is a little bit short.
I am very confused now, what is a word for dress and what is a word for skirt. Apparently duo uses them interchangeably.
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
I think he meant to say 这条裙子有一点儿短. And yes, in this sentence you can actually say 有一点儿短, or 有一点短, or 有点儿短, or 有点短. Same thing.
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 有 is necessary when it's used as an adverb (to describe an adjective) however.