Typescript: Narrowing Problem

https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgKoGdrIN4ChnLAAmAXMumFKAOYDc+yIcAthGRVSHQ3EUVBHTp2lGvQC+uXKEixEKAOJQA9gFcADjgbUVGgHIs25UVwlSA9ACpL+S8gAKKgEYAbCM1vmpCZSArIYVRAEMGBfAFEADxZ1N2QAXmQACjgyDCwAH2QlNXUASgSAPi0CAmAYJIBCOAA6JlY87GRzc2QAWmLwqBUoMkdldWgwAE9kAHJ6iDHkImVBRmUwZAhI4H9fZBHB8ZyNMZqGUtKfPyXXOHPzhORayfojo5P-GGVla9rie4eCJ7O4KHeNV4-EE6C+BEkklwVhsyDsAGVlC5VKENgBGTy4X4BIIhMIgKIxNxo64pNKYAFZXb5IolUotZBomoYo7lKopG7oNAUvJ1QyNQ4PbGXFwXUWkuCc7nQXl3QWPXzPV4SqXpKC8z7y46Kv4AxIcuBctW84ECITg5BQo4MpkAJkFbMqBqNPL5DTw3x+Os27nUAEEVYbpeqLQrTsgRWLJYlIMx-W6IKHteGXm8Y76-TVNZ7kML-tdY-HTaCLZCpNDrLZkIjkaiQMh7XCvNi1mrSaoKeTMtldPkyB2sGtg7SPaUBGBVFB60kBwCg8aE8hKvFEkEiBAYKAIEQzFjvYFgnXCXG3LaJV3KT3cgV4sVR2UKq2KSk8gKc8LRZHAXL3-vlYkPh3LUvXDJx8wAoE+DNMFBTLCxKzhaskRRfFkAAZkxPcU1xI9ohPCA0PPYcqV7G87wdCoACJJkowh6zgN9PQ-KMrggn8mL-NMbizIDf1A8DuOLc1YNwKEYSrGsUI2AAWdo2mQAALMAwHUYQWmoYAwAU1QnBqHxmHMZhgAQFR0GUGAwHMAAVYZBnhEzgHUSy1nQVRBHMAA2aSAHZpMxA88Q2AxumUAB3AAeKzlkiSAQCILkACUABpkAS64ggAaxAMKQEKJIADc4GRIwEryMhDQpMAuUK4rCC5KLsChbEAtwokIFk-VUmIq8NDIukH3ZSV51dSZGO+YKVAitU8oYpMQP8SNWO49jvma-9uOzDj+L1QSoJLETJCAA