TTI metric wrong? (main thread looks busy)

Have an interesting result here where the ‘first interactive’ time seems to come WAY too early from looking at the ‘Page is Interactive’ graph.
That graph shows a lot of main thread blockage all the way past 50 seconds with no contiguous 5 second interval between the red lines. Here I’m assuming each red line is 100ms worth of main thread blockage and the definition of the TTI metric is 5 contiguous seconds of no blockage.

Here is another example: [url=]WebPageTest Test - WebPageTest Details
How can first interactive be at 32s?? Looking at the ‘Page is Interactive’ chart there is a ton of activity on the main thread between 30-45 seconds - there is no 5 second period of inactivity there - especially around 30 seconds.
How can this be??? thanks!!