It isn't possible to draw any credible conclusion from your single result - especially one that is unexpected.
In my experience, eating fat with carb slows down any rise in blood sugar. For some, it results in a modest rise, but the ride lasts longer. For some it just means there is a delay before a rise. There are of course other factors that could be in play - like your activity levels after your buttery toast, whether your blood sugars were rising or falling before eating your toast and a few others. Some also would find their blood glucose might rise again in the period after your graph.
All of that is very simplified.
To be honest, if you want more of an insight, you would have to repeat the exercise a few times to see more credible trends.
In any case, your meandering from 5-andabit to what looks like 7-andabit wouldn't be medically alarming.