That's the baseline they've been using forever. Whenever the protocols are discussed about limiting the change to 2°C, that's what they mean. They've been warning about the dangers at 1.5°C for many years.
It's not an attempt to mislead anybody. They're simply leaving out the "above pre-industrial levels" part that they've said so many times they assume it's not necessary. Especially on HN, where the headlines are sharply limited in length.
Headline should be: "World now likely to hit 1.5 °C rise above pre-industrial levels in the next five years".