Yes, it's probably being used as an uncountable noun.
Many countable nouns in English can be turned into uncountable nouns just by using the singular without an article. Then you're talking about the idea or the thing as a group rather than about individuals.
"The high school I attended is in New York." I am talking about one particular school. This is an ordinary singular.
"Students usually learn algebra in high school." Now I am not talking about one particular school, but about high schools in general.
As I say, you can do this with many nouns.
"Mr Putin heads the government of Russia." He is the leader of one particular government.
"Mr Putin discussed his theories about government." He is speaking of government as a general concept.
But you can't do it with any noun.
"I ate a large banana." I ate one particular banana.
WRONG: "Banana is curved and yellow." No, you just can't do that with "banana".
I'm not sure if there's some general rule about what specific nouns can be turned into concepts and which can't.