You needed to check your allies itemizations. You are aware that high mmr players are constantly checking opponents items throughout a game, as a carry they often do it while they hit jungle camps. Its also important to check your allies to see their item timings. You have an idea of how the game should be going at different timings throughout the game. You are aware of general timings for heros to reach items i.e. am hits a 15 min treads bf. But sometimes timings get skewed based on lane performance and rotations that either help or hinder certain heros timings. When you have a good game its important to realize your networth lead isnt indicitve of your entire teams networth lead, and vice versa when you are behind.
