Are you failing to spot the "Some of its seats were designed to fit to the crossbar and that instructions were provided." Also European Safety Standard EN14344 covers three seat types only one of which is designed to fit in the top tube. I ask again "Why the Gaffer tape?"
No shoot Sherlock!!! They also sell seats that mount behind the saddle so of course only some of their seats are designed to fit on the crossbar. And of course EN14344 covers other types of child seat too. The fact is they do sell them and they are covered by the standard. But it seems that people here are not able to see beyond the gaffer tape despite all the press articles on it saying the seat was bolted and taped to the top tube.
Looking at the Leco seat I might well add something extra to fix it in place. You have either the choice of doing it up really tight and risk denting the thin top tube or leaving it a bit looser and risk the seat moving and scratching the top tube and paint. Which of us hasn't used the occasional bit of tape, inner tube or zip tie to supplement the manufacturer's fittings?