I just looked it up and read through some examples. It happens so often it makes perfect sense that it has a name... but it never occurred to me that it did before now.
I've done the same, and I'm still not quite sure how it compares to the description of "something important being interrupted by something insignifcant", unless it's
meant to complicate the situation. Those seemingly less signifcant characters who unknowingly tamper with the plans of the big players.
After all, isn't it telling that I did notice the character in the ice cream scene?
It wasn't done for comical effect, and she wasn't just an unwanted customer, she was also a (potential) unwanted witness who could prove to be a (potential) flaw in the killer's perfectly orchestrated crime.
And this episode was literally crammed with all kinds of occurences and fact-establishing stuff in order to prove that the killer was lying (actually, to prove that the victim's death wasn't an accident).
From the far-fetched type of water examination (which usually only works in an autopsy setting "the victim was supposed to have drowned in the sea, but there's no salt water in his lungs"), to the schedule of the ice cream vans, to the American tradition of buying ice creams only at certain times of the day (
really??), to the distortion of the radio signal, to the possible involvement of a secretary who was employed for only a few days.
There was almost something desperate about it so perhaps it was interesting and ironic that
the one thing that didn't happen turned out to be the proof Columbo was looking for.
Ultimately, it only proves the suspect had been lying about his whereabouts, it doesn't automatically pin him at the alleged crime scene.
Sure, to go through great lengths to fabricate an alibi during a crime investigation is going to look suspicious, to say the least, but a good lawyer should know how to twist things in favour of his client.
But these episodes are never about "what happens next". It's all about the confrontations.