How did 'velcro' get translated to 魔术贴 ('magic attachment??')
魔术贴 is not a translation or transliteration of Velcro. It is a 'Chinese name' given to the product.

Terms like 魔术(Magic) or 神奇(wonder),  are commonly used in naming new and innovated products. 


What is so wonderful about the Wonder Bra? -- unlike normal bra, it wonderfully pushes your breasts up 
What is so magical about 魔术贴? -- unlike normal sticker, it can be easily peered off like magic