At least in the United States (and I'm pretty sure this is true around the world), facts and information cannot be copyrighted. Just because a work is copyrighted, doesn't mean every part of that work is copyrighted, and factual information conveyed by the work is a part which is not subject to copyright.
Copyright on a collection of facts is limited to the selection and arrangement of those facts, and only if that selection and arrangement has some bare minimum amount of originality. See Feist v. Rural, 499 U.S. 340. In this case, it looks at first glance like the person who made that site made their own selection of which materials and which sources would be included; the one place where they really seem to have copied their selection is from glass catalogs with datasheets from specific manufacturers, who would have a hard time arguing that "everything we manufacture in this widely-recognized class of substances" is an original selection. What the author of the website has done is relinquish his rights in his selection and arrangement of the data.
In some places, there are other rights besides copyright that do apply to databases; for instance, the EU recognizes database rights to protect significant investment in compiling a database of stuff. But the US does not have that concept.
For citing stuff, that's not really a legal question, and has more to do with academic standards. Ask your adviser or teacher if you have one.