It seems fairly common for someone to become well known for something they stumbled into. Their fame catches them by surprise. Why is this?
One reason may be that it’s hard to plan to be well known. You need to be in the right place at the right time. If you see something taking off and decide to become an expert in it, it may be too late to become famous in that area.
Another reason may be that fame is determined by how others value your work, which could be very different from how you value your work. Something you find only incidentally useful on the way to another goal may turn out to be very valuable to others. This is fairly common, as I discuss here.