A hero is a man (when defined in a text such as the epic poem Beowulf) who is easily recognized as such when one simply looks at them. Therefore, it is no surprise that when the herald and the sentinel lay their eyes upon Beowulf they immediately recognize him as a hero.
Upon landing on the shores of Hrothgar's Dane-land, the sentinel states the following:
"Never have shield-bearing men so openly landed, nor do you know our clan's word of passage, or hold my folk's consent—never have I seen in the world a warrior like that one among yourselves—a hero in his armor! He is no henchman, unless his looks deceive; he has a regal bearing."
Knowing that Hrothgar and his Danes are in the midst of fighting a terrible foe, Grendel, the sentinel welcomes Beowulf and his men. The sentinel sends Beowulf and his men to meet with the herald to be announced to Hrothgar.
Once Beowulf and his men come upon the herald, the herald comes to the same conclusion as the sentinel had.
"By their war-gear they appear worthy warriors, and
their leader, a hero who led his band hither, is surely a valiant man.”
Therefore, the sentiments of the sentinel (from chapter three) reiterate the feelings shown by the herald (from chapter five).
Chapters referred to come from the E-Text of Beowulf and the E-Notes link below refers to the lines the quotes have been taken from.