The sentence is a complex sentence.
A compound sentence is one that has two independent clauses joined by a coordinating conjunction. In a compound sentence, the two clauses could as easily be written as two independent sentences.
We went for a walk, but it was raining.
They boarded the train, and the conductor blew the whistle.
A complex sentence is one that has one independent clause and one or more dependent clause(s) connected to it by a subordinating conjunction. In a complex sentence, the dependent clause needs the independent clause for meaning.
We stayed at home because it was raining.
They boarded the train since the conductor blew the whistle.