I think that person said that because at a quick glance the helmet shape and a few other bits look similar, but if you really look there are a lot more differences than similarities. I think it's the colour as well XD Very nice, I like the detail on the top and sides of the helmet and the shoulder insignia.
someone actually said looks like Master Chief? he looks NOTHING like Master Chief! and besides there's like 3 versions of Master Chief as well as countless SPARTAN versions so which Master Chief were they talking about?
Someone will always compare your artwork and characters to something well known and popular, just disregard it; everything has already been done. This is a cool design with interesting details but I would streamline the silhouette and stance, he looks like he's standing very awkwardly, and doesn't tell me anything about the character by the way he holds himself. The legs might be a bit too short compared to the arms and overall body, I am reminded of the saying that it's always better to err in favor of longer legs, rather than short. If you're unsure what length they should be, they're better off too long than too short.