I think many are aware now, but it was indeed a widely held misconception that Raya is the New Year among the Chinese. In fact, even till now Raya is sometimes referred as Malay New Year (the literal translation of 馬來新年) in the Chinese speaking community, though not officially, but common enough to keep the misconception alive.

One of the reasons might be that for the Chinese people, the New Year (Spring Festival) is generally the most important - thus most greatly celebrated - occasion in a year. And as we observe how Raya is celebrated, especially in relative to other occasions, it's perhaps not too surprising that we assume the same it is for the Malay/Muslim as well.

Indeed some Chinese have the same misconception about Deepavali with the Hindus.

And I think in general we're doing better now, including in education - sad to say, but I don't remember my teachers (in SMJK) bothered to teach or clarify this with us when we're growing up (another reason the misunderstanding was rife) . But I think many Chinese are more respectful in this regard today.