On my desktop computer, I browsed to my.yubico.com (the link without the additional information). It brings up the following in Yubico's demo website:
"YubiKey NFC
You are here because you have scanned your YubiKey over NFC and the NDEF tag in the key is programmed with this URL. The captured string is presented below and can easily be copied to the clipboard to use it somewhere else.
If an OTP is read from the URL you can also validate it against the YubiCloud."
So, it does appear to be OTP related. But, if I were using OTP, I'd expect the key/phone combination to send the OTP code directly to whatever was active on the screen. Not go to a Yubico web page where it could be copied and then pasted into the required field. But, then again, I don't have any experience or knowledge of OTP.