About: http://webisa.webdatacommons.org/80731425

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	You are right that the sentence is a declaration, but the complement of the verb was is a question, and that does demand a question mark -- which convention holds overrides" the period.
http://www.w3.org/ns/prov#wasQuotedFrom	stackexchange.com