It’s unlikely that was connected with missing one Metformin tablet, or connected to your cuppa (though depending on how your body behaves, and if your liver begins releasing glucose as soon as you rise, you might find that you may see a difference immediately on getting out of bed, and 45mins later.
I think it’s more likely to show how your body is reacting to the carbohydrates in your meals. It would be worth considering reducing the portion of potatoes/beans (or maybe choosing either/or rather than both?), and considering a smaller portion or a slightly different breakfast?
But as you say, it’s worth double-checking to see if these results are a general trend, or just a one-off.