I'm back @thegoose.
So I love these cases because I think it's when you really see flex "flexing" it's smarts (LOL). I don't know if you noticed, but when your flex ran Wednesday, it ran for a shorter duration for each zone than it typically does. While flex does not usually change durations, it had to do a "mini watering" on Wednesday because the incredibly high evapotranspiration your plants were experiencing. If it didn't do that, it would have dropped below your allowed depletion line. I think it's pretty cool stuff.
But to answer you question more directly, it decided to water so much today because your ET was just so incredibly high, I'm assuming this is due to how hot it is. How long have you been using flex? Has it worked well for you in the past? If it's been working well for a while, I would recommend keeping an eye on it and just "filling" the moisture levels on the zones that look like they don't need water for the next week or so. It may be that since we cap saturation at 110%, we didn't accurately capture all that could rainy moisture you got. If this is a newer schedule, you may want to adjust your sun/shade setting on the zones that seem like they were watered when they didn't need to be. Sun/shade works as a "tax" on ET, so this can be used to crank that down a bit, without affecting anything else.