solo harmonica study 3 - exemple 1.2 - video

hi

i was watching the vi'deo from soloharmonica stdy 3, exemple 1.2 

around 0:45 is said:2 blow, 5 blow, 8 blow....those are the major third of the four chord.

i think i may had or had not understand that.

in a C harmonica those notes (2 blow, 5 blow, 8 blow) would be E correct?

in the second position, c harmonica, we would be playing in the key of G, so the fourth chord would be C, the major third would be E, correct?

i understand it correctly or there is some mistake?

thanks!