The pine tree in the middle is taken from Maine's ensign and is a prominent symbol of Maine.
The pine green stripe represents Maine's forest.
The star in the top left is taken from Maine's old flag and represents the North Star, which itself symbolizes Maine's motto, "Dirigo" (meaning "I lead").
The buff is taken from Maine's old flag.
The red symbolizes the state's presence in New England.
I've honestly never thought of the Mexico comparison, though I can kinda see it now. I think the buff center and the pine tree are enough to differentiate it from the Mexican flag, though I may flip the green and red.
The tree design was taken directly from Maine's ensign, and the star position came from Maine's old flag. As for the Texas point, the lone star is used in other U.S. state flags, like those of Arizona and California (and North Carolina but that one does just look like a Texas flag ripoff), so I don't think it's unfitting to use it here, especially since it was on the old flag.
He seems to really like "Maryland-style" flags, which just have a ton going on all over the place. I don't really like those kinds of flags, though honestly New Brunswick's isn't that bad. The top and bottom strips each stick to a solid color on a solid background (yellow on red for the top and white on blue for the bottom). I'm not a huge fan of the middle strip with the ship — I think it would be better if it stuck to solid color on solid color like the top and bottom — but it doesn't use that many colors and goes well with the water.
My own Maine flag redesign (media.kbin.social)
🎄 Grey Grades Canada's Flags! (And Merry Xmas!) 🎄 (iv.ggtyler.dev)