It compares something to a noun the way 처럼 does, but casually and often with a hint of mockery: running around the practice room like an ostrich, answering as if it were a job interview, as invested as if they were on the ride themselves. Strictly speaking 마냥 is an adverb meaning endlessly, and this comparing use is treated as nonstandard, but it is everywhere in speech. Use 처럼 when you write.