It looks as though the 'Boarder' refers to the Pupil on the line above
Anthony McCall is in a separate house from the family above signified by address on left hand column and \\ to the left of his name
I did think that maybe the 'boarder' was in relation to the 'Pupil' in the entry above, but why write the 'boarder' bit in Anthony's square of that census field, it could have been squeezed in on the same line as 'pupil'?
The thing I cannot wrap my head around is if he was renting and living in the house, just him and his family, why even put boarder on the entry, no one else seems to if privately renting a house without the landlord/lady actually living in the accommodation as well, it doesn't seem a necessary thing to add.
The only other scenario I can come up with is if the landlord/lady he was boarding with might not have been in the household when the census was taken?