Angela does not say what the measurements are in the video, but I paused and looked at the marks on her ruler and/or mat, and I figured out the sizes: she is working with a bunch of 4 7/8", 4.5" and 2.5" squares. She makes some HSTs from the 4 7/8" squares (each block uses 3). She makes some units where the 2.5" squares are used to snowball 2 adjacent corners of the 4.5" square (each block uses 4 of these - 2 light ones, and 2 dark ones). The block also uses 2 plain 4.5" squares (1 light, 1 dark). (Personally, if I was going to make this block/quilt, I would use 5" squares to make the HSTs and then trim them down to 4.5" size - I get better HSTs this way and I don't have to deal with cutting on a 7/8 line.)
I highly recommend trying out one block with some scrap fabric to check that the measurements are correct before doing a lot of cutting!