Bringing the high down is one thing. Having a flat line, with less than 1 degree deviation, for the whole day is another! Or perhaps "low" isn't calculated this way.
I think you're technically correct, but "low" and "high" are often just used as shorthand for "what temperature it will be in the morning" and "what temperature it will be in the afternoon," respectively. A weather app may just be reporting the expected temperature at 8 AM and 3 PM, even if there are lower lows or higher highs at some other part of the day.