Is it legal for a landlord to throw a tenant out on heresay?
There was no proof of what is being accused. Allegedly there was marijuana in the apartment.
Whether or not the landlord was justified in terminating the lease of a given tenant depends upon what the lease states for ending it and whether or not the lease was for a term or a month-to-month.
Hearsay is a legal term for the courtroom to keep evidence out at trial. From what you have write, it the landlord believes that illegal substances were being used at his or her rental, the landlord may have been justified in terminating the lease that you are writing about regardless if true or not.