It's not really a stretch to say that ancient China was familiar with roman civilization. The two were major global powers at the time, and China's naval history was pretty well established even as far back as 722 BCE.China traded Silk to the Roman empire through the historical Silk Road pretty frequently. The silk was in high demand since romans initially knew very little about how it was produced, but silk clothing was pretty luxurious at the time. As for this historians description you have to realize this was translated from chinese, and even then it's a description of roman culture coming from someone that was alien to greek and roman culture and customs. It seems to me when he's describing things like "They could breathe fire from their mouth, and juggle bulls" someone probably witnessed a big roman celebration or performance with trained performers and didn't know enough about the culture to know it was a massive celebration..
He mentions at the end that he's never even seen the regions himself, and that his notes are all second hand accounts anyway.