What claim is sampson making about himself and anyone from the rival house of montague?

That not a solitary Montague can make him to go to the "weaker" side of the wall.

The House of Montague in Romeo and Juliet is one of "fair Verona's" two fighting families - the House of Capulet is the other rival. Montague's child, Romeo, falls for the girl of Capulet and they run off much to the outrage of their particular families.