Is my dean/teacher allowed to be following me on twitter?

[Hannah]

Ok sooo. There was this huge incident where "twitter beef" was brought up. Some girls were arguing and i made a couple of remarks and statements. When i got to school the next morning he told me "you need to stay out of things before you get in trouble too" i asked him wat he was referring to and he said my exact tweets . I was pretty freaked out but i just laughed it off. However the next day in school when i was walking down the hallway he said "your tweets were a little better last night" again, i just laughed but this time it was pretty freaky. Im not sure, but it doesnt seem like its legal for him to do that because isnt that like an invasion of privacy?

Ps.... Me and my friends think he made a fake account so we wont know who he is .