This is the 4130th most frequent Russian word.
прямо
Directly; straight; openly.
The word 'прямо' in this context means 'straight', describing the direction he went.
Он пошел прямо по улице.
He went straight down the street.
Here, 'прямо' is used to mean 'directly', implying speaking honestly and without avoidance.
Скажи мне прямо, что ты думаешь.
Tell me directly what you think.
In this case, 'прямо' functions as an intensifier, meaning 'just' or 'truly' emphasizing the degree of amazement.