Bluetooth LE uses a client/server (called "central" / "peripheral") model; think of "server" like "web server", typically the client is your smartphone.

I could believe that a single peripheral can't simultaneously connect to multiple centrals (I'm just getting started with BTLE), but the typical pattern is for e.g. the heart rate sensor and smartwatch to both be peripherals of a smartphone.

The first article you reference says: So for folks that may use one device for cycling and another for running, this could cause issues if both devices tried to connect to the heart rate strap at the same time.

As long as you're not cycling and running at the same time, this isn't an issue.